Stores files under DATA/ in the packed tar
Adds file-format.md
Adds Python 3.4 to travis configuration

Also, fixes compilation warnings.
Merge branch 'master' into 'unpack'

Adds DATA/ in the packed tar.
Allows 'reprounzip graph' to read a pack
Fixes classifiers for reprounzip
Adds more system info to 'runs' section

This is needed to correctly select a Vagrant box.
Merge branch 'master' into 'unpack'