Updating docs with boolean array indexing and nonzero order. 

Small docs update of boolean indexing in the user and reference manuals and at *np.nonzero* to close #3177. Also adding links to *row-major* and *column-major* terms where found. 
We try to use the same colors for all bike sheds, that way they are easily recognizable.  When there doesn't seem to be uniformity, pick the color that seems best and use it everywhere.