This avoid overwriting portions of our log output when using Flake8
in verbose mode.

Closes #193

Diable multiprocessing behaviour on Windows

*Description of changes*

Due to https://bugs.python.org/issue27649, while Flake8 can *run* with multiprocessing on Windows, it does not behave as we expect it to behave. To provide the best experience that is in agreement with our documentation, we must disable multiprocessing until https://bugs.python.org/issue27649 is fixed and released.

Closes #184

See merge request !105

Due to https://bugs.python.org/issue27649, we cannot continue to
expect multiprocessing to work as we expect and document it on Windows.
As such, we are going to revert back to our previous behaviour of
disabling it across all versions of Python on Windows to provide the
default expected behaviour of Flake8 on that Operating System.

Allow plugins that are on by default to be ignored

*Description of changes*

Previously, users were unable to ignore the error code of a plugin that was on by default. This adds a tiny bit of extra logic to re-enable that behaviour.

*Related to:*  #195

See merge request !104

Previously, to ensure that plugins on by default were reported, we
added them to the select list. This means that ignoring them became
impossible. To accomodate our reporting logic and a user's ability
to ignore, we need to keep our select and extended select lists
separated.

This allows us to have a better understanding of who is selecting what,
where, and how and make our decision as to whether or not an error
should be reported more wisely.

Closes #195

Fix hyperlink in Links.



See merge request !102

Raise exception when entry_point not callable

Raise exception when entry_point not callable

E.g.:

```
$ .tox/flake8/bin/flake8 mobileweb
Traceback (most recent call last):
  File ".tox/flake8/bin/flake8", line 9, in <module>
    load_entry_point('flake8', 'console_scripts', 'flake8')()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/cli.py", line 16, in main
    app.run(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 316, in run
    self._run(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 299, in _run
    self.initialize(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 289, in initialize
    self.find_plugins()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 143, in find_plugins
    self.check_plugins.load_plugins()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 375, in load_plugins
    plugins = list(self.manager.map(load_plugin))
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 267, in map
    yield func(self.plugins[name], *args, **kwargs)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 373, in load_plugin
    return plugin.load_plugin()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 173, in load_plugin
    raise failed_to_load
flake8.exceptions.FailedToLoadPlugin: Flake8 failed to load plugin "P999" due to Plugin <module 'teamcity.flake8_plugin' from '/Users/marca/dev/git-repos/teamcity-messages/teamcity/flake8_plugin.pyc'> is not a callable. It might be written for an older version of flake8 and might not work with this version.
```

This is nicer than the previous behavior of raising an obscure `PicklingError` and then hanging.

```
$ .tox/flake8/bin/flake8 mobileweb
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 268, in _feed
    send(obj)
PicklingError: Can't pickle <type 'module'>: attribute lookup __builtin__.module failed
```

*Related to:*  164

See merge request !101

E.g.:

```
$ .tox/flake8/bin/flake8 mobileweb
Traceback (most recent call last):
  File ".tox/flake8/bin/flake8", line 9, in <module>
    load_entry_point('flake8', 'console_scripts', 'flake8')()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/cli.py", line 16, in main
    app.run(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 316, in run
    self._run(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 299, in _run
    self.initialize(argv)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 289, in initialize
    self.find_plugins()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/main/application.py", line 143, in find_plugins
    self.check_plugins.load_plugins()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 375, in load_plugins
    plugins = list(self.manager.map(load_plugin))
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 267, in map
    yield func(self.plugins[name], *args, **kwargs)
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 373, in load_plugin
    return plugin.load_plugin()
  File "/Users/marca/dev/git-repos/flake8/src/flake8/plugins/manager.py", line 173, in load_plugin
    raise failed_to_load
flake8.exceptions.FailedToLoadPlugin: Flake8 failed to load plugin "P999" due to Plugin <module 'teamcity.flake8_plugin' from '/Users/marca/dev/git-repos/teamcity-messages/teamcity/flake8_plugin.pyc'> is not a callable. It might be written for an older version of flake8 and might not work with this version.
```

This is nicer than the previous behavior of raising an obscure `PicklingError` and then hanging.

```
$ .tox/flake8/bin/flake8 mobileweb
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 268, in _feed
    send(obj)
PicklingError: Can't pickle <type 'module'>: attribute lookup __builtin__.module failed
```

See #164

Sort reports by line and column

*Description of changes*

The reports have been incorrectly sorted. This fixes the sorting order to use the line number and then column. It also adds a test to verify that the sorting algorithm works.

*Related to:*  #196

See merge request !100