Added parallelism to IDT code.  Woo!

Stuff goes much faster now.  Need to apply this elsewhere!
(Mostly) Functional bathy module with tests.

This module uses the ComputeProximity algorithm from the GDAL library
to generate the bathy data.  The Go bindings fail to pass the progress
function properly between the Go code and the C code, causing errors
to be thrown.  The workaround is to build the GDAL library from source
after removing the references to the progress functions in
alg/gdalproximity.cpp and then copy those libraries into place.
Added Knob functionality.

Eventually most of the carto tunables will use this type.
Minor cleanup in utils module.

Removed unused stuff and pulled unnecessary int() cast.
Modified extents to call new gdal package.

Until the bugs in lukeroth's gdal package are fixed, I'll be urnning
out of my own branch.
Accidentally fixed maxdepth in bathy.

Better now!
All four layers generated correctly!

Landcover, elevation, bathy, and crust are all generated correctly.
Next steps: clean up debug code, handle files sanely, and build a
better test.