Split executable from library

This splits the implementation from the main file. I.e. the hpc executable is now only a small wrapper around the library which has been added in the cabal file.

This refactor is required to implement a testsuite for the implementation which can depend on the library.

app/Main.hs

+module Main where
+
+import qualified HpcMain as HPC
+
+main :: IO ()
+main = HPC.main
\ No newline at end of file