doc: project -> Zephyr Project

To make the documentation readable from the source I want to get rid of the
substitutions for the project name an code name. This does not add any values
and makes it unreadable when looking at the text files directly. It also causes
some issues when people use those without actually knowing what they represent,
resulting in some weird and redundant language.

Change-Id: Icc70eef90966ed19531c3406fe7a6d1866f7d81d
Signed-off-by: Anas Nashif <anas.nashif@intel.com>