The new version uses category as the reference point to later infer the
issue number and counter value.
As a consequence, it will return (None, None, None) if the base name
doesn't contain a valid category.

The new parser allows using file names like '123.feature.1.ext' which
are convenient when one wants to use an appropriate extension (e.g. rst,
md) to enable syntax highlighting.

* Fix the use of -mtowncrier. twisted#163

* Apply suggestions from code review

* Update src/towncrier/test/test_project.py

Co-authored-by: Glyph <glyph@twistedmatrix.com>

…n - close twisted#165

    This allows for the towncrier to be seamlessly used in non-python projects

Co-authored-by: Kyle Altendorf <sda@fstab.net>

Co-authored-by: Kyle Altendorf <sda@fstab.net>