Migrate docs to RST with Sphinx

[matthewhughes934]

An attempt at moving to Sphinx for #26

• Convert HTML documentation to RST

  This is just the result of:

  $ mkdir docs/
  $ pandoc --from=html --to=rst --output=docs/index.rst imaplib2/imaplib2.html
  $ rm imaplib2/imaplib2.html

  I haven't look too closely at the result to see if there was anything imperfect in the conversion, but I'm planning to later consolidate documentation between the pydocs and what's here, so I might wait for that, rather then potentially updating some docs that may be removed soon; the goal is to just start with something.

• Create sphinx project for documentation

  Just followed a basic setup via running sphinx-quickstart, then combining the current docs with the bare index.rst that was generated. Some headings were altered just to bring them all up one level. Include a .gitattribute to preserve the line endings in generated make.bat

  All other added files are just the result of this auto generation.

  Sphinx: https://www.sphinx-doc.org/en/master/index.html Which is suggested by RTD: https://docs.readthedocs.io/en/latest/intro/getting-started-with-sphinx.html

  To sample the docs locally:

  $ cd docs
  $ pip install --requirement requirements.txt
  $ make html

  Then point your browser at /path/to/imaplib2/docs/_build/html/index.html. The requirements to build the docs(just sphinx) are listed under docs/requirements.txt

[codecov[bot]]

Codecov Report

Merging #30 (938d89f) into master (11dbeb0) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #30   +/-   ##
=======================================
  Coverage   12.38%   12.38%           
=======================================
  Files           3        3           
  Lines        1413     1413           
=======================================
  Hits          175      175           
  Misses       1238     1238           

Flag	Coverage Δ
py3.6	12.38% <ø> (ø)
py3.7	12.40% <ø> (ø)
py3.8	12.43% <ø> (ø)
py3.9	12.43% <ø> (ø)

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[piyueh]

Awesome! I will be away from my computer until the coming Wednesday. Let's see if @graingert can review/merge this PR. Otherwise, I'll work on it on Wednesday.

[piyueh]

Thanks! https://imaplib2.readthedocs.io works now!