Add a program with 2 parsing errors and 1 warning

Sometimes it's needed to do quick tests to verify that the parsing
warning/error reporting logic is not broken. This MIPS64 source file will be
useful in those occasions.
Add compiler warnings output to all targets
Add compiled docs output dirs to .gitignore
Remove the obsolete (and ugly) class ErrorOutput
Fix compilation warnings and do some clean-up

* use parameterized generics where needed;
* if it is not possible, then suppress warnings;
* use foreach iteration in some places;
* other minor fixes.