Use bnfc-meta to define a parser

[pascalh]

bnfc-meta provides an easy way of defining parsers. Unfortunately it doesn't provide support for source locations (yet). Hence, this task is only about proving an example parser on how to use bnfc with astview. Probably just use the javalette example language.

For now it might make sense to just ignore the syntax highlighting for the generated language (and maybe add it later on in a separate task).