Wrapper for 'gmt which' #92
Description
The wrapper should be a function in gmt/modules.py. See how other wrappers are built in gmt/base_plotting.py.
This module will be useful to download the new GMT tutorial and topography data using the @filename syntax. For example, running for the first time gmt which @tut_quakes.ngdc will download the data to the GMT hidden folder and provide the file name to stdout. We will use this to make a higher level gmt.datasets package that loads these data as numpy arrays and xarray grids.
The wrapper will need to capture stdout and return it. See discussion on #43