fixing documentation about previous singleton argument

[galonsky]

I think this documentation is wrong. The new behavior is the same as setting singleton=False because that's the flag needed to NOT share data across instances, right?

Looked at the old documentation:

Alternatively, you can create an instance that does not share data with other instances, by passing singleton=False to the constructor.

[coveralls]

Coverage remained the same at 96.027% when pulling 83e852a on galonsky:patch-1 into ed422fc on jamesls:master.

[bmerry]

Thanks for catching this!