Previously, the following fields on Diff instances were assumed to be
passed in as unicode strings:

  - `a_path`
  - `b_path`
  - `rename_from`
  - `rename_to`

However, since Git natively records paths as bytes, these may
potentially not have a valid unicode representation.

This patch changes the Diff instance to instead take the following
equivalent fields that should be raw bytes instead:

  - `a_rawpath`
  - `b_rawpath`
  - `raw_rename_from`
  - `raw_rename_to`

NOTE ON BACKWARD COMPATIBILITY:
The original `a_path`, `b_path`, etc. fields are still available as
properties (rather than slots).  These properties now dynamically decode
the raw bytes into a unicode string (performing the potentially
destructive operation of replacing invalid unicode chars by "�"'s).
This means that all code using Diffs should remain backward compatible.
The only exception is when people would manually construct Diff
instances by calling the constructor directly, in which case they should
now pass in bytes rather than unicode strings.

See also the discussion on
https://github.com/gitpython-developers/GitPython/pull/467

It usually fails on branches, which doesn't help
assessing PRs.

Adding support for git remote set-url/get-url API to Remote

Don't choke on (legitimately) invalidly encoded Unicode paths

I see no need in verifying the status code.
It's enough to just get the error.

Both commands enable handling of a little known feature
of git, which is to support multiple URL for one remote.
You can add multiple url using the `set_url` subcommand of
`git remote`. As listing them is also handy, there's a
nice method to do it, using `get_url`.

* adding set_url method that maps to the git remote set-url command¶
 * can be used to set an URL, or replace an URL with optional positional arg¶
 * can be used to add, delete URL with kwargs (matching set-url options)¶
* adding add_url, delete_url methods that wraps around set_url for conveniency¶
* adding urls property that yields an iterator over the setup urls for a remote¶
* adding a test suite that checks all use case scenarii of this added API.¶

Signed-off-by: Guyzmo <guyzmo+github@m0g.net>

Please exclude the particular assertion instead.

Related to
https://github.com/gitpython-developers/GitPython/commit/a3f24f64a20d1e09917288f67fd21969f4444acd#commitcomment-17691581

Add test case as example of Git commit with invalid data