Add satpy's resampler classes to pyresample

[mraspaud]

Problem description

Satpy implemented a series of high level resampler classes that would fit better as an upgraded interface to the different resampling methods in pyresample.

The basic workflow with these classes is:

resampler = Resampler(source_geo_def, target_geo_def)
result = resampler(data)

This is related to issues #181

[djhoese]

New thought: Could/should we have a classmethod on the base resampler class to do the above code in one call?

NearestResampler.quick_resample(source_geo_def, target_geo_def, data)

Possibly even do (source_geo_def, target_geo_def, data1, data2, data3) to resample multiple data arrays.

[mraspaud]

Fine by me, but it doesn't need to be implemented together with this though.