adding utils/asainterpolate.py and tests for it;
also adding skip functionality in the tests if
missing datasets req'd by test.
 On branch regrid
 Changes to be committed:
	new file:   paegan/utils/asainterpolate.py
	new file:   tests/test_asainterpolate.py
	modified:   tests/test_dataset.py
	modified:   tests/test_depthvar.py
	modified:   tests/test_roms.py
	modified:   tests/test_timevar.py
adding change to requirements.txt
editing readme to include scipy and numpy 1.7, and higher versions of netCDF4
 missed a line
implemented get_values_on_grid on the base Dataset class, that uses the CfGeoInterpolator
test passing for rgrid 4d regrid
test passing for rgrid 4d regrid
adding a basic netcdf writer abstraction to ease the code writing in the dataset and roms methods
adding the asaregrid utility
roms regridder, working, and writing to new file
Merge pull request #59 from asascience-open/regrid

Addition of regridding functionality