keep option

[stuartpb]

I'm thinking a keep item in the dict, with paths (sort of like how patch has files), would be a nice extension to the format - one that says not to touch certain files in the current source tree (not deleting them or overwriting them).

Among other things, this would make Pull Tool really useful for managing projects with separately-retrieved dependencies or other assets, like Node.js scripts: a problem I ran into the other day was that I used Pull Tool to retrieve a new version of a script I was working on, and I lost not only the currently installed node_modules, but all my cached data... and all the sibling data I intended to run the script on.

This would also be a nice and simple solution for a lot of #21's use cases (just drop the file into place once and then put it into keep).