Derive scopes with additional methods about fusion

[dphfox]

One gotcha here is merge conflict handling. It's entirely possible that the outer scope defines some method with the same name as one which the inner scope would like to have. scoped throws an error on merge conflicts, because it's likely programmer error there. However, in this case, it would be forming an implicit contract with the owner of the outer scope that they don't use methods of that name. This breaks encapsulation, so I would suggest that merge conflict errors should only occur for methods that are passed in simultaneously, not between an inner scope's method definitions and an outer scope's method definitions.

[dphfox]

Implemented - just need to write docs.