Fix support for namespace handlers

[rdumont]

What I wanted to do was to have a handler (along with description, args etc.) directly under a namespace. These are the two issues that were found and fixed:

1. In the namespace handler there was always one arg missing from the left. Now all args are being passed appropriately.
2. The help function threw an exception when trying to deal with a namespace that is also a command. Now it doesn't, and the command is being documented as expected.

[guifromrio]

That looks great :) Thanks!

LGTM

[guifromrio]

Ah, can you also update the README? :D