Support subroutines and functions

[stadelmanma]

These shouldn't be too hard because I'll only need rules for the first and last lines.

Additional details, apparently everything can have a contains block

• http://www.lahey.com/docs/lfpro78help/hh_goto.htm?hh_start.htm#F95LSProceduresFun.htm
• http://www.lahey.com/docs/lfpro78help/hh_goto.htm?hh_start.htm#F95LSProceduresInternal.htm

I think the best practice might be to generalize the contains "section" and just share it across derived types, functions, subroutines and modules. This will allow some technically invalid statements but generate a simpler grammar.