Better support for XMLs with no release events (and therefore no format)
Fixing bug with quotes in format URL. Adding ZIP file output. Might switch to that or SQLite storage.
change releaseIndex to metaIndex and store entire metadata. then, change references to releaseIndex to calls to getRelease(), a new function that will take the release ID, and call getRelease() on the appropriate metadata. Also replacing references to Catalog.releaseIndex in 'catalog-cli.py' with implicit calls to Catalog.__contains__()