Ribcage-environments completed. That was actually really easy
Added a vector-add-left command. Returns a vector that is the old vector with a new item added on to the front
Eh, changed vector-add-left to vector-add. Adds to the end. Makes no big difference, but more consistent with how memory should probably work.
Merged changes in interpreter.ss. Also fixed use of if-exp where if-true-exp would be more appropriate.