Remove `bytestring-class` dependency

The `bytestring-class` package won't build on recent versions of GHC without
adding build flags. Since our usage of it was minimal anyway, we can
just fold in the needed functionality (i.e., one small function) and remove
the dependency.
Merge pull request #2 from ThoughtLeadr/remove-bytestring-class

Remove `bytestring-class` dependency