Add lexer for NuSMV/nuXmv model checker language

[deme3]

This MR adds support for the nuXmv/NuSMV/SMV model checkers input language.

nuXmv is a superset and an enhancement over the NuSMV model checker, both of which developed by Fondazione Bruno Kessler, a research institute in Trento (IT). In turn, NuSMV originated by Carnegie Mellon University's "SMV", a symbolic model checker supporting CTL.

Not sure if relevant to the scope of reviewing the merge request, but fyi: Language reference is in User Manuals for both programs, which are listed here: https://nuxmv.fbk.eu/documentation.html.

Adding this language, it being a superset of the two previous languages mentioned, will virtually add support for all of them. (Note the aliases provided by the lexer are in fact: nuxmv, nusmv, and smv)