Represent Booleans as mode Bu internally
Create FIRM graphs for Minus and handle extended Int literals
Merge pull request #155 from jspam/056-bye-bye-modeb

Fix two more TODOs in the FIRM constructor
Implement field access

I only just realized that fields need to be handled differently
depending on whether they're used as lvalues or rvalues. I'll handle
that when we can actually assign things to them