Create namespace.rst

Proposed informational REP on driver namespaces.
Renamed to be REP 135
Posting to ROS users on 20/Feb/2013
Forgot to change REP number inside text.
Added references to discussion for REP 135.
Making REP 135 active.
Merge pull request #22 from chadrockey/namespace

New REP 135 for Driver Namespaces Merging as Active