Use decorator design pattern

[yossigil]

on fanyEBNF. nullable, get first, follow, etc. should be in decorator(s)

[OriRoth]

@yossigil Done in 2938d28a0696812c4386b1cb9eef49d94f36a18c. See new hierarchy in classes EBNF and FancyEBNF. Language test cases now use EBNF instead of FancyEBNF. If it is to your liking, close this issue, comment otherwise.