subcommand support

[tolidano]

the ability to delegate top level commands easily to entirely separate command instances is valuable.

i.e. top-level maps to a command and evaluates 0 or more sub-levels. all remaining tokens to be parsed for that command are what's left.

it should be easy, given that tokens are taken as a parameter and $_SERVER['argv'] is only taken otherwise, to create commands which take the "unparsed" part of parse (but parse must know about these subcommands up front, to avoid creating arbitrary unnamed anonymous options).

notes: nategood/commando#20

[tolidano]

can also leverage this: https://github.com/nategood/commando/pull/80/files