Added two seperate files that is required for the Clifford Algorithm to be implemented.

1) The general clifford algorithm py file
2) The py file that allows us to run a basic Gaussian elimination
Added two new files which provides the functionality required for the
clifford algorithm used to compare quantum graph states.

clifford algorithm.py consists of the main algorithm
gaussian_elimination.py provides an algorithm for a gaussian elimination,

which is required in the Clifford Algorithm
Merge branch 'master' of https://github.com/tanhaoqin/QuantumGraphState into clifford