added dms2decimal function
added strike_direction function to dtopotools
several improvements to topotools to allow returning x and y as 1d rather than 2d arrays and to do a better job of plotting topo, especially with imshow option: split into masked arrays for B<0 and B>0 with different colormaps.
Merge remote-tracking branch 'mandli/topotools' into topotools

* mandli/topotools:
  Initial commit of topo module containing base topography classes
  Convert to using new topotools
  Correct degrees to latitude conversion
Add tests for topo objects

Adds tests for topo objects.  Also includes some bug fixes for said
objects.  Note that this commit still does not include support for
topo_type 1 even though the tests for them exist.