Local attributes

[Jengamon]

Right now, this only accepts the local attributes, but doesn't do anything with them. As is, this would lead to incorrect behavior, as const and close change some of the mechanics of how assignments work/are allowed, while any other values should be rejected.

Goals

• [x] accept local attribute syntax
• [x] reject invalid attributes
• [x] implement const attribute
• [ ] implement close attribute (along with the __close metamethod)

[Jengamon]

In the tests/goldenfile.rs you will see a module collected_print which is a clone of the print from the io implementation except it collects the output to throw it in a channel. I think this might raise the question of how to handle the io module.