Move macro parsing to a separate process

[eteran]

I'd like the make macro processing an independent process, where interaction with the current buffer or window would be done via RPC. This has a few advantages:

1. If for some reason it crashes, we won't lose all of our work
2. If it is hung, it is trivial to kill the process
3. isolates the code into an independently manageable project
4. allows drop in replacements with ease (I'd like to have lua or python as options, see issue #2 )