Start expanding aliases on their own
Add variables expansion
Simplify import dispatching
Start locals expansion
Expand tuples and other special forms
Expand quote
Handle remote calls
Implement pending tests
Expand ^var
Expand super
Improve compilation times and memory consumption

This commit includes three changes:

1. Previously, the parallel compiler released at once all processes
   depending on a particular module. This commit ensures they are
   released according to the number of cores available. This ensures
   we have fewer modules being compiled at once

2. Garbage collect the current process every time we are waiting
   for another module to be compiled

3. Do not compile a module for files that simply define modules
No need to require for requires for all expansions
Rename DispatchTracker to LocalsTracker
Delay some error handling to translation
Expand comprehensions
Expand requires and imports
Fix build
Simplify and fix bugs around lexical scope on try
Make sure IEx r helper does not return a record

The tuple r/1 returns can be a record and IEx will try to inspect it.
Tag the tuple so it will be inspected as a tuple.
fix typo in URI docs

URI.decode_query returns a `HashDict`