Splitting off +linops into a separate submodule

Squashed commit of the following:

commit a24665d7e1b4be5f44d0901e9b0ff1a2f84f23a5
Author: Zhengyun Zhang <zhengyun@smart.mit.edu>
Date:   Tue Dec 2 11:43:33 2014 +0800

    moving +linops into a submodule