Improve help documentation (C-h m)

Now the emacs help looks like this but with better spacing:

<pre>
Typed-Clojure minor mode (indicator Typed):
The official minor mode for editing Typed Clojure. Provides
namespace typechecking, error navigation, display of type data,
and annotation snippets.

key             binding
---             -------

C-c		Prefix Command

C-c C-a		Prefix Command
C-c C-x		Prefix Command

C-c C-a f	typed-clojure-ann-form
C-c C-a v	typed-clojure-ann-var

C-c C-x f	typed-clojure-check-form
C-c C-x n	typed-clojure-check-ns
</pre>