Initial implementation

* Python 3.4
* Use argparse for command and argument parsing
* Use Python syntax and semantics in manifest configuration file (avoids
  need for custom parser)
* KISS, leaving as much as possible to metadata layers
* Don't wrap git commands, leaving repository and submodule management to
  plain git commands

Signed-off-by: Esben Haabendal <esben@haabendal.dk>