Store and retrieve big files in chunks

Swift "large objects" aren't enough because:
- dynamic large objects don't ensure the integrity of the uploaded data
- static large objects are not even supported on hubiC
Support checking and removing chunks
Retry transfers up to 3 times if the Swift token expires
Basic tests powered by Bats
Enable exporting Swift credentials to a file
Handle network errors during authentication
Add tests to handle corrupted data
Upgrade rauth and swiftclient
Port to Python 3

Using 2to3 + 3 fixes
Bump version number to 0.3
git-annex-remote-hubic v0.3