Add script to compress and back up Prairie data
Change baseDir to scriptDir, for clarity
Produce directory mirrors for TIFF and ZIP outputs

The script now takes three arguments: base input directory, a TIFF
output directory, and a ZIP output directory. The TIFFs are written in a
directory structure that mirrors the base directory, but beneath the
TIFF base. The ZIP file generation is analogous, in the ZIP base.
Add a quick note on how to execute the script
Use 2GB memory limit by default
Fix potential mangling bug in zip directory name