Add: local as a possible ref
Add: Caller to the error object
If a function that throws an error was originally called by a named logic function, the name will appear in the caller property of the error response.
Fix: include caller variable in the solver
Fix: provide local as empty if not provided
Fix:  remove ability to inject functions of the clues object
Injected functions lose their reference to the object.  The functions can be reached through the `this`  (or the injected `self`)
Add: express-clues in the utils subdirectory
Release: 2.0.0