0.4.0 bye bye SUB

- removed SUB function, same can be achieved using functions now
- updated tests and docs to reflect removal of SUB
- don't recursively interpret return from top level function patch
- pass merge fn as second arg to scope function for convenience

0.3.0 SUB and DEL through syntax

- a function in a patch works acts like SUB, thanks @foxdonut
- undefined in a patch acts as DEL
- updated tests to handle new syntax
- fixed edge case where function patch wasn't resolved
  happened when function patching deep into an object that doesn't exist in the source