Deprecate pkg_resources

Merge pull request #19 from kiwicom/mk/deprecate-pkg-resources

chore(deps): Deprecate pkg_resources.

v0.10.0

• chore: remove coala check
• feat: remove Python 2 support
• feat: remove Python 3.6 support
• feat: add support for Python 3.9 and 3.10
• chore: upgrade requirements
• refactor: remove dictalchemy package

v0.9.0

• feat: Warn if use_decimal if not used with simplejson
• refactor(ci): switch to GitHub actions from GitLab CI
• chore: reformat code with black
• chore: Upgrade test requirements

v0.8.0

fix(dependencies): Pin dependencies to keep it working with python 2.7

* pinned more-itertools to < 6.0.0
* pinned pytest to <= 4.6.6

Newer versions dropped support for python 2.7