Fixed a null pointer exception in fieldUpdate for Maps.
Some renaming and restructuring
- ErrorMessages => Errors
- Moved all static messages to a subdirectory Static
Added dynamic errors for all exceptions at the Rascal level.
Replaced Java exception ArithmeticException by the Rascal exception
ArithmeticException
Continued adding concept pages for exceptions.
Merge branch 'master' of https://github.com/cwi-swat/rascal.git