util: Finish gen_deltarepos_file()
Small refactoring
Add compression constants into deltarepo module's __init__.py
DeltaRepos: Add more comments, add more unittests, fix few bugs
Tests: Add new test data
Tests: Update fixtures.py
Tests: Add a test repodata for an empty repo (repo_00)
Tests: Update fixtures.py (Add new paths)
util: When sha checksum is specified, use sha1 (just like classical createrepo) + few other small fixes
Tests: Add unittests for util module