Added FITC functionality

Added the FITC functionality very similar to GPML Matlab toolbox.  Had
to rewrite all the covariance and mean functions to fit the format.
Also, fixed a bug in covNoise.  The code is much slower now, and will
need to be improved.  Especially in the FITC inference.  I deviated
away from a speedy implementation for clarity.
FITC Approximation

Encorporated the FITC approximation for GP.  Utilized the gpml matlab
code base as a template.  Rewrote all of the covariance functions to
support this.  Also rewrote all of the mean functions to support this
as well.  Added a demo_FITC file
Total Rewrite (includes literal port of gpml MATLAB)

Total rewrite.  Implemented all funcitonality to replicate both
demoRegression and demoClassificiation (with hardcoded inputs).  Need
to optimize the code (with things like linalg.solve_triangular for
cholesky solves).  Also, need to implement a "real" cholupdate
(currently does a full Cholesky).  Need an optimization capability that
works.  min_wrapper doesn't seen to converge to minimize.m  Also, need
a better directory structure and an object oriented way to call the
covariance, mean liklihood and inference functions.
Merge pull request #5 from mathDR/master

FITC Implementation