* Add font and background colors to Style

* Move all styles to get_style_defs, add tests

* Remove hardcoded styles, add special lineno style

* Add styles for special line numbers in tables

* Update noclasses documentation

* Refactor linenos elements and styles, add tests

* Update AUTHORS

* Fix multiple CSS prefixes, add tests

* Remove Python 2 compatibility

* remove 2/3 shims in pygments.util
* update setup.py metadata

* Remove unneeded object inheritance.

* Remove unneeded future imports.

Unittest classes are kept - for now - since py.test is ok with them.
Generator tests had to be switched to pytest parametrized tests.

Resolves #1492

Custom Lexer/Formatter File Loading

This introduces support for some missing features to the Handlebars lexer:
Partials and path segments. Partials mostly appeared to work before, but the
`>` in `{{> ... }}` would appear as a syntax error, as could other
components of the partial. This change introduces support for:

* Standard partials: `{{> partialName}}`
* Partials with parameters: `{{> partialName varname="value"}}`
* Ddynamic partials: `{{> (partialFunc)}}`
* Ddynamic partials with lookups: `{{> (lookup ../path "partialName")}}`
* Partial blocks: `{{> @partial-block}}`
* Inline partials: `{{#*inline}}..{{/inline}}`

It also introduces support for path segments, which can reference content in
the current context or in a parent context. For instance, `this.name`,
`this/name`, `./name`, `../name`, `this/name`, etc. These are all now tracked
as variables.