Add dead code elimination, statement chaining to Myrial

- [x] Use a control flow graph for storing Myrial programs during compilation
- [x] Implement liveness analysis for the control flow graph (http://www.cs.colostate.edu/~mstrout/CS553/slides/lecture03.pdf)
- [x] Implement dead code elimination
- [x] Implement statement chaining.
- [x] Remove DUMP statement from MyriaL