Misfit.subset accepts bool arrays

Before it required a list of indices because it took the number of data
by `len(indices)`. Taking that away allows using bool numpy arrays which
are faster to create.
Moving window solution for Euler deconvolution

Enabled by a MovingWindow class that takes an Euler instance and runs it
on moving windows. Keeps only a specified percentage of the best
estimates (by using an estimated error like in ExpandingWindow).
Merge pull request #85 from leouieda/euler-window

Moving window solution for Euler deconvolution