Made cabal package/build scripts; added VML imparse grammar.

Updates:
* the /Haskell directory now contains all the files necessary to build
and package for release a Haskell implementation of Verificare
functionality (libraries and an executable);
* made minor adjustments to Promela abstract syntax definition;
* added starting point for Promela parser;
* added VML imparse grammar definition.

To-do:
* pick a license for Haskell package (if desired).