Add Erlang lexer implementation

Mostly taken from https://bitbucket.org/birkenfeld/pygments-main/src/7304e4759ae65343d89a51359ca538912519cc31/pygments/lexers/functional.py?at=default#cl-1617

See #30
fix warning about unescaped ] in character class
add fuzzy guessing if -module(foo) is seen
Merge branch 'erlang'