Added batch processing script and reorganized repo.

Reorganized repo to match the structure of QIIME and other related projects: scripts are under a scripts/ directory and library code is under the fresco/ directory. The README has been updated with instructions for how to install fresco. I also renamed ```fresco.py``` to ```fresco``` because Python was getting confused between the ```fresco``` module and the ```fresco.py``` script. It's generally a good idea to not have the .py extension to script names anyways, so there shouldn't be any issues with this renaming.

Added a new script ```submit-fresco-jobs```, which submits batch fresco jobs to a cluster. The code is very specific to Minerva, and only a very basic script interface is provided (the rest of the behavior can be tweaked from within the top of the script file itself). This can be cleaned up and generalized later, but for now I think it's worth adding as-is so that we can start processing the various datasets.

The script generates many batch scripts (one per fresco job) and submits them to the queue (with a 1-second delay between each job submission, as per @cleme's suggestion). If the script is run over the same input/output directories, it will only submit jobs for which there are not already results. This allows us to support efficient reruns of the script in case some jobs fail mid-way through the sweep. The script itself does almost no processing / heavy lifting; it simply generates cluster jobs and submits them.

I've tested this script on Minerva using the Crawford mice dataset and it seems to be working.

Fixes #14 #20.

@rybern can you please review?