Steenzout.sphinx

- made sed expression on `apidoc` target alpine friendly
- updated dependencies
- `sphinx_rtd_theme==0.4.2`
- `click==7.0`
- `colorama==0.4.1`
- `Jinja2==2.10`
- `Sphinx==1.8.2`
- `setup.py` now works with `pip` version >= 10
- fixed copyright range
- test on Python 3.7

- removed `sphinx.ext.imgmath` extension since it causes problems with [readthedocs.org](https://readthedocs.org/)
- docstring change

- automate apidoc generation as proposed https://github.com/rtfd/readthedocs.org/issues/1139

- initial release
- templates for
- `conf.py`
- `Makefile`
- `steenzout-sphinx-generate` command-line interface