Wrapped the bodies of the match methods.

This was done so that all the clauses
would be neatly listed.
Replaced ints with constants in the term directions.
Added id argument to One/TwoSiteOperators, currently set to None.
Created a new method:  withNewDirectionAndPosition.
Added id equality checks to TwoSiteOperator.
Now computeOneSiteExpectation iterates over the tags.
Now the id slot in the terms is mandatory.
SpareOperator --> SimpleSparseOperator
Created new SparseOperator functions that take lists of terms.