Added LIMIT clause test file and fixed syntax of LIMIT clause.
Improved limit test (removed view, added comments and non-limited select). Added transformation to always limit things up to 50 if no stricter limit is present.
Added subquery to test. Fixed syntax so pretty-printer automatically prints parentheses around a subquery.
Added empty file as test. Changed syntax to accept 0 or more statements. But it doesn't accept the empty file yet :\