Update comments about thread safety
Merge branch 'pbkdf2-iterations-vary', remote-tracking branch 'origin' into log
Add LOGLEVEL_SCHEMA to tuf.formats

log.py previously checked the format of log level arguments with LENGTH_SCHEMA.  LOGLEVEL_SCHEMA might be clearer.
Update comments and schema type checked

Expand the comments on 'logging.Formatter.converter' to discuss the converter attribute.  Modify LENGTH_SCHEMA to LOGLEVEL_SCHEMA.
Reword comment and fix typo in ed25519_key.py
Update README.md
Update AUTHORS.txt
Update the valid expiration data
Merge pull request #123 from theupdateframework/log

log.py updates
log.py changes reviewed by both Trishank and Monzur.
Merge branch 'develop' of https://github.com/theupdateframework/tuf into integration-tests-python3
Merge pull request #124 from theupdateframework/integration-tests-python3

Updates to integration tests
Python 3 compatibility changes to the integration tests reviewed by Zane.
Merge branch 'develop' of https://github.com/theupdateframework/tuf into ed25519
Update ed25519_key.py following Monzur's review

We now raise an exception instead of blindly passing.  The previous behavior of expecting the caller to verify the availability of PyNaCl is not ideal.

Expanded the comments related to hexlifying data.

Renamed create_in_metadata_format() and create_from_metadata_format().