Basic indentation and font-locking support for EBNF language files.
 http://en.wikipedia.org/wiki/Extended_Backus-Naur_Form

 Refer to ebnf2ps.el for language description/variables to customize
 syntax.

 This mode uses '.' as rule ender and ';' as comment starter.
 (TODO: support different rule endings [.|;] and comment starters?)