Fix reference to global app
Pretend we're using a "rake" compiler

This is useful for introspection in a QuickFixCmdPre autocommand, for
example.
Support config/projections.json

Looks like projections might be the only real use case for editor.json.
Document projections front and center
Allow alternate files with %m to bubble into related

I'm toying with unifying these.
Support custom rake tasks in projections