vendorize libcflib

[CJ-Wright-Citadel]

I think the code is only using the diff part of libcflib, which can be an annoying dep.

[mariusvniekerk]

simplest approach is probably just to make a pr with a git subtree addition of libcflib. This allows relatively easy updating to the vendored library whilst still allowing for easy updates from upstream which may happen when conda changes some of the formats in the future