Fix METADATA generation for git dependencies with extras (#1129)

* fix METADATA generation for git dependencies with extras

* add comment

* add comment

* add comment and linting

* Move trailing space from `base_pep_508_name()` to `to_pep_508()`

* Merge remote-tracking branch 'origin/master'

# Conflicts:
#	tests/packages/test_vcs_dependency.py

* Make changes python2 compliant

* Handle any type of marker

* Insert space before semicolon in dependency.py if vcs