deps pinning prototype 1 (#146)

[kkimdev]

Maybe something like this? wdyt?

[floooh]

I'll try to set aside some time and play around with this early next week.

I think it would make sense to have a separate command to create a snapshot file (./fips pin or ./fips lock). And then may be when the imports are read (e.g. here: https://github.com/floooh/fips/blob/master/mod/dep.py#L99) it would check if such a snapshot file exists in the top level repository, and fix up any revs in the imports dictionary with the revs from this file...

This way fips fetch and fips update should automatically do the right thing... (at least that's the idea) ;)