Packaging for Debian

[Rupan]

This PR adds a first stab at Debian packaging. I've left some fields, notably much of the copyright file, as-is for the upstream maintainer to touch up as appropriate. I'm not an expert at this, and I am aware that there is Sphinx documentation, but I couldn't quite figure out how to make it work with the dh build system.

Oh, and I've added some minor bug fixes as well -- missing cassert includes and a config parameter for the Sphinx docs.

[codecov]

Codecov Report

Merging #26 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #26   +/-   ##
=======================================
  Coverage   97.62%   97.62%           
=======================================
  Files          27       27           
  Lines         970      970           
=======================================
  Hits          947      947           
  Misses         23       23           

Impacted Files	Coverage Δ
include/pog/automaton.h	100.00% <ø> (ø)
include/pog/item.h	98.27% <ø> (ø)
include/pog/parsing_table.h	92.95% <ø> (ø)
include/pog/tokenizer.h	97.84% <ø> (ø)

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