[Feature request ] - Derivative templates

[bsless]

Creating an entire template to get a few small changes on top of an existing template seems like unreasonable overhead, and following our discussion on Clojurians Slack, I came to the idea of derivative templates - a derivation is defined in terms of the "delta" over an existing template.
This also allows creating a sequence of derivation, each a function of the last.
Derivations need to account for the transformation fns and file changes.

• transformation fns: chain all of them
• file changes:
  • if a file with the same name exists, override it
  • if a .diff or .patch file exists, apply it

And that's how you make "epochal" functional templates.
WDYT?