initial download package
first implementation of metadata downloader/parser
changed downloader to save repomd.xml
added ability to download and checksum verify remaining metadata files
changed downloader to save repomd.xml
added ability to download and checksum verify remaining metadata files
changed checksum value to hex_digest for greater consistency with haslib (and not to be super vague)
first pass at primary parer/generator
a couple of comments
initial pass at a packages downloader
initial test script
removed test portions from modules
separated out parsing of primary.xml and downloading to see where the time is being spent
changed back to http protocol and default max_concurrent parameter
Added pages for the export distributor, and the ISO importer and
distributor.
Added some technical documentation for importers and distributors.
Consolidate several docs files together to form a better heirarchy.
Clean up technical documentation.

Also, move some ISO importer default values into settings in
constants.py.
cleaned up, documented, and commented current download package
Several fixes in response to jdob's PR review.
Merge pull request #135 from pulp/rbarlow_export_docs

Rbarlow export docs
changed test to pass the generator through to better mimic the final control flow of the downloader