apply expend(expection=True) recursively for Add instances. Added expression attributio to Expectation class
Merge branch 'master' of http://github.com/jrjohansson/sympy-quantum-notebooks
moved Expectation and Covarianve to sympy repository
Merge branch 'master' of http://github.com/jrjohansson/sympy-quantum-notebooks

Conflicts:
	sympy_quantum_extra.py