boulder/cli: Implement update command to update version in recipes

[joebonrichie]

trafficstars

Updates an existing recipe (stone.yml) with a new version and tarball, provided by the user. Additionally, it recomputes the hash of the new tarball and increments the release.

PoC only, to do this properly we need a write function in moss.source.format, that enforces desired formatting. We can already easily parse the recipe.

[ikeycode]

i havent forgotten about this just so you know =)

[joebonrichie]

Dropped dyaml for something that worked. Had a look at moss.format.source, it's very easy to parse and update the values, not so easy to write them back to disk.