Using cabal test and accept list parsing works.

Rather than having two separate cabal projects in order to produce a
testing executable, the project now relies on Cabal's test-suite
functionality. The tests can be executed with `cabal test` after
configuring with the --enable-tests option and building the library.
Passing tests no longer log themselves. It would be nice to switch out
test-framework for Cabal's detailed test suite, but right now that
causes a linking error.

Parsing a list of Accept media types without quality types now works as
expected.