Merge pull request #217 from vladimir-v-diaz/develop

Support Python 2 + 3
Add py26, py32, py33, py34 to setup.py.
Merge pull request #218 from vladimir-v-diaz/develop

Initial implementation of authoritative delegations.
Merge pull request #219 from vladimir-v-diaz/develop

Remove tox.ini dependency, improve pycrypto_keys test coverage, and add missing download.py docstrings.
Merge pull request #220 from vladimir-v-diaz/develop

Allow proper loading of partial metadata, update requirement files, and minor edits to repository_lib.py and integration tests.
Merge pull request #222 from vladimir-v-diaz/develop

Add missing test conditions to test_repository_lib.py and minor edits to modules
Merge pull request #223 from vladimir-v-diaz/develop

Add missign test cases to download.py and updater.py.
Acknowledge the NSF.
Added switches to the generate script

Added two switches to the generate script:

  -k (or --keys), which forces the creation of new keys.
  -d (or --dry-run), which skips the actual writing or copying phases

The second option might be useful in the future, and helped me debug the
optparse module, so I left it there.
Minor cosmetic edits to schema.py.
Minor cosmetic edits to sig.py and util.py.
Minor cosmetic edits to formats.py
Merge branch 'generate_switches' of https://github.com/SantiagoTorres/tuf into SantiagoTorres-generate_switches
Move optparse import statement.

Organize import statements of standard Python and TUF modules into separate blocks.
Merge branch 'SantiagoTorres-generate_switches' into develop