add docs

[casperdcl]

• gh-pages: https://docs.iterative.ai/shtab/
  • put all of README into organised website
  • auto-generate API reference & add source links
• fix README logo
• update repo metadata & description
• auto-deploy docs on release

caveats

• "Edit" button gives 404 on generated pages
• follow-up: replace README sections with links to website

[codecov-commenter]

Codecov Report

Merging #51 (93d9365) into master (5d17c85) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #51   +/-   ##
=======================================
  Coverage   88.80%   88.80%           
=======================================
  Files           3        3           
  Lines         250      250           
=======================================
  Hits          222      222           
  Misses         28       28           

Impacted Files	Coverage Δ
shtab/__init__.py	92.19% <ø> (ø)

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[jorgeorpinel]

@casperdcl sorry for the delay. Did you want the docs team to review this one for clarity/ copy edits/ etc?