v8: makeRests(inPlace=True) returns None for scores

[jacobtylerwalls]

Let makeRests(inPlace=True) return None for consistency with other methods (and with itself).

[coveralls]

Coverage decreased (-0.001%) to 93.261% when pulling c081f61 on v8-makeRests-return into 5381ab6 on master.

[mscuthbert]

@jacobtylerwalls -- i've debated making inPlace just return the same thing as not inPlace in v8 because it'd help the typing a lot. BUT I don't like what it does to the doctests.