Extracted macros to a separate crate

Had to expose docopt::parser module and a few methods in docopt
Fixed build system and examples

Made examples to rely on docopt_macros crate. Also fixed documentation
and readme.
Merge branch 'master' into split

Conflicts:
	docopt_macros/src/macro.rs
Hide parse module.

We may have to export it (for now), but don't publicize it.