This pull request contains lexer for Robot Framework http://robotframework.org test data. It addition to lexer itself it contains an example file, needed changes to mappings, etc.
It turned out that Robot's test data syntax was not too easy to parse using regular expressions and thus I decided to inherit directly from Lexer. Trying to cover all/most special cases made the code pretty long and I thought it would be better to keep it in a separate _robotframework module. The lexer class is nevertheless exposed via the other module.