add ...rest patterns to macros, and test structs

[ExpHP]

Closes #100

In addition to adding ... I also did the following:

• Move the macros into their own file, which is the first module declared in core/lib.rs. This is common practice to help dodge issues related to the fact that macros must be declared before they are used.

• I ported over the test structs from funky. These are just a bunch of types like A, B, C, ... that help reduce the barrier to writing unit tests by not requiring the author to be so inventive with types from the standard library. I missed having these during the last couple of PRs...

• Added a test to verify beyond any doubt that the macros are reexported by frunk, because... I actually was very surprised to see this happening! Apparently this is a special feature of pub use crate_name::*?

[ExpHP]

@lloydmeta can I pull the switch on this or do you prefer having the chance to review everything?