make type determination more flexible. #8

Some usernames may be first.last, which get_type currently thinks is a hostname.

argument types should possibly be pluggable, or possibly plugins should be able to set allowed types to a regular expression.

For username specifically it should configurable from the main configuration file. Username is the only current type that is site specific.

Also, I wonder if expanding the api to support type specific get_info functions may be a good idea...

so a plugin class could implement...

get_info_ip(arg):
get_info_hostname(arg):

rather than having plugins do it themselves:

get_info(arg):
    t = get_type(arg)
    if t == 'ip':
        ....
    elif t == 'hostname':
        ....