Improve tool ui

Small fixes to improve the user-interface of tools.

* nit_dir is more robust and display errors if invalid
* option --nit-dir is really needed
* remove useless and buggy --clib-path and NIT_CC_PATH
* nit does not collect options after the program file but let as options for the interpreter
* 3 -v to show class-level information, 4 -v to show property-level information
Isn’t this line too long? I know some people feel that a 80-characters limit is too short, but this line end at the 229<sup>th</sup> column.