PRISM input and output support

Implement support for the PRISM language (http://www.prismmodelchecker.org/manual/ThePRISMLanguage/Introduction) as an input and output formalism (i.e. lexer and parser for PRISM code, conversion from PRISM models to automata models, conversion from automata models to PRISM models, and formatting of PRISM models back to PRISM code).