Add Hackage badge to header and make badges flat
Hide join from Prelude in order to fix GHC warning
Port to hsc3 0.15
Update copyright notice
Bump version to 0.9.0
Show Travis CI badge for develop branch
Use fromNonNegative instead of fromIntegral

The code with `fromIntegral` doesn't compile with QuickCheck-2.7.1 on Travis.
Bump version to 0.9.1