started to rewrite command.py
made it better
renamed vars
supported more metavals
make metaval have more elasticity
fixed the bug if it has an alias for nothing
rewrited the get_usage
fixed a bug if arg_default is None
fixed bug while printing exception
avoided complain
rewrited the most of the function in command.py
removed ScanError
supported aggregated arguments now
fixed the doctest
fixed the bug of the single char options
added mode_flags
renamed arg_alias_map
reanmed mode_flags
refactored a lot
renamed scan