Added as_ndarray and tests

as_ndarray() is a convenience function for getting rid of memmap objects.
It can also be used to convert an array, with the minimum possible copies.
Optimized apply_mask()

Added usage of as_ndarray() to avoid codying data in some cases.
Fixed a bug in as_ndarray(), added test for it.
Array order related optimization in apply_mask()

Order of arrays is now taken into account by apply_mask(), to improve
on execution time. When a memmap is received by apply_mask(), it is
copied with the most appropriate order. A keyword argument has been
added to force the order in case the heuristic fails.
Merge remote branch 'nisl/master' into mask_optimisation
Faster smoothing in apply_mask()

gaussian filtering has been tuned to get higher speed.
Output of apply_mask() is now always in F order (which is good for
subsequent operations, because timeseries are contiguous in memory)
Removed a spurious non-ascii character.
Merge pull request #44 from pgervais/mask_optimisation

apply_mask() speedup