delete old .hgignore file
Eliminate name shadowing warnings; turn up warnings.
some Cabal file cleanup
Get the library installing again.

The 'properties' and 'nqueens' test suites use the 'propositional'
library, which is a library I haven't released to hackage.  For the time
being, comment out those two test suites.
add link to GitHub project in cabal file
More cabal file cleanup.
add a minimal description to the cabal file
add a README for GitHub.
git ignore more stuff