Convert more expressions to IR, and implement converting IR to SSA form.
Fix some warnings in ccross.
Add some comments to ir/mod.rs
Change where ccross emits semicolons, to (hopefully) appease clang.
Fix list.mh to work despite the language regressions that have occured in the last day :P
Add += operators, and once again have assignment expressions have the value of the assignment instead of unit.
Include %=, and actually include assignment operators other than just += in the parser.
Clean up compound assignment operators