Fix identation
Inverse sample update and sample rescaling

If during a long time there is no update, the weight could be NaN if the
rescaling is done after the update, and locking the value in the sample.

When rescaling before, in that case, we invalidate all data as the weight
will set to 0
Merge pull request #8 from razrin/master

Fix exponentially decaying sample in case of long period of inactivity