Wrapper around SFrames SFrame.

Work in progress, most functionality missing

1. Install Cxx, the Julia C++ FFI.
2. Clone and make a debug build of SFrame
3. Set an environment variable SFRAME_PATH to the directory that SFrame was cloned to. By default, it is assumed to be in a folder called SFrame in your home directory.
4. Then just type using SFrames in your Julia REPL. Ssee the tests for usage.

SArray([1,2]) + SArray([3,4]) == SArray([4, 6]  # true