RFC: snapcraft sources keyword for parts

[robert_joslyn at selinc.com]

> well, or you could simply maintain the patches in a github (or
> launchpad) tree in a forked upstream branch that you use in your
> snapcraft.yaml ...

This works too, of course, but I was hoping to minimize changes to an 
existing internal infrastructure where this isn't easily done. If this 
isn't a common issue for others, I can deal with it on my end (and 
probably restructure things to make it easier).

Thanks,

--
Robert Joslyn
Software Engineer, R&D - Automation
Schweitzer Engineering Laboratories
509-332-1890 ext. 3214