Replace reset with Enter on layer 2

I keep hitting reset when selecting an item in LaunchBar
Be more specific with make

This wires up dependencies for all the build steps to ensure that the
keyboard layout is completely rebuilt when anything changes.

This also includes documentation of the core make targets.
Fix modifier plus keypress magic number

After the all_usb_keys merge this now types right modifiers instead of
left modifiers so only works by accident.  Now it types left modifiers
as described in the documentation.
add new home layer 3
add modified layout.h file