Merge branch 'develop'

* Move the metadata from `setup.py` into `setup.cfg`.
Added `pyproject.toml`.
Removed `setup.py` - it is no longer needed.
Got rid of tests erroroneously finding their way into the wheel.

* Started populating version automatically from git tags using `setuptools_scm`.

* Migrated the metadata into `PEP 621`-compliant `pyproject.toml`, got rid of `setup.cfg`.

* test build in develop and pull requests

* use static version instead of dynamic git tag info

---------

Co-authored-by: KOLANICH <kolan_n@mail.ru>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "markdownify"
-version = "0.13.0"
+version = "0.13.1"
 authors = [{name = "Matthew Tretter", email = "m@tthewwithanm.com"}]
 description = "Convert HTML to markdown."
 readme = "README.rst"