Implementing dependency management

[binkiklou]

Dependency management is well documented in the specifications, although the way they going to be implemented is left for debate. The feature needs to have a working test, in the test folder.

[dekrain]

Dependency management will be oriented about symbols exported from a translation unit (a Chirp source file), and then imported into another translation unit's scope.
To do this, we need to track symbols used by the program, which already has been mostly done by me.