It would be helpful to run bin/test.sh locally without having to install
dependencies of hpc-coveralls. Instead we can install hpc-coveralls
independently and use it after installing it once.
To be able to use an internal test library, we need to have it as a
separate package. See comments in streamly-benchmarks.cabal for details.
Use a test library for common test modules
Also, added "opt" flag to control optimization levels.
Add a README for tests.
Update benchmarks readme.
