refactor scopes and add top-level and block scope (related!)

- annotate delimiter pairing logic
- generate a var statement for the given node
- [FIX!] update scope to use positions and call .type() recursively!

this fixes the following code:
```coffee
import x from "./lib/coffeescript/index.js"
do ->
  x = 3
  x
```
- rename "scope" to FunctionScope
- break out a separate TopLevelScope so we can look at modules more clearly
- add lots of TODOs and fix namedMethod?()
- remove extraneous 9e9 limit from .splice call
- add quite a lot of notes to compileWithDeclarations
- add block scopes!!!!
- imports and exports are so much better supported now!!!
- assigning to an imported symbol is an error