fix: rewrite statement splitter

[psteinroe]

this pr rewrites the statement splitter so that it passes through all postgres regression tests.

closes #135

todos:

• introduce Repeated syntax definition to parse CTEs and UNION etc better
• add support for multiline comments in the tests (and check if the parser properly parses them too)
• make the tracker return false by default if a position reached the end of the definition and by that, require an AnyTokens to be the last in every definition. this will make the TABLE my_table syntax work much better
• dont skip any regression tests anymore