Added a dozen string checks
Added several sizeViolations
Inverted the tables describing the checkers

Each checke now lists the AST constructors for which it has to be
appplied.

Before actual checking starts, this table is inverted and changed into
tables that map AST constructors to sets of checks.
Removed redundant "node ast" argument from all checkers
Moved management of check states to separate module
Added missing imports of new CheckStates module
Updated overview

- new measurements
- added CheckStyle measurements
- updated implemented checks
Adding/improving comments
Merge branch 'master' of https://github.com/cwi-swat/rascal.git