Replaced np.zeros with faster np.empty
Fixed wrong assertion about scaling of data.
Removed .rst source from docs.

It is distracting and not useful for our audience.
Fix segment_dat, so it deals with nonexisting markers in dat properly.

Added unittest and docstring.
Fix segment_dat, so it ignores epochs which are not properly sized.

this is usually the case when the marker is too close to the border of the data.