Add a .gitignore file.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
add testsuite-related gitignore entries
Bump `base` constraint and convert changelog to MD
Fix-up 94e1aa6f621df46 re changelog name

The changelog file was renamed but the .cabal file wasn't updated to
reflect that rename.
Bump upper bound for `deepseq`

The upcoming `deepseq-1.4.0.0` version's changes don't affect `parallel`
so we can safely bump the upper bound
Add Hackage-shield to README.md