Misc. prep for codegen

• Delete old codegen code
• Draw basic block and fork join nest edges in dot visualizer
• Make array constants always zero
• Compute reduce cycles, fork join placement
• Cleanup (get rid of IRDisplay, simplify code now that array constants are always zero (parsing))
• Comments in IR text
• Verify a partitioning is valid
• Compute various analyses on partitioning

hercules_cg2/src/lib.rs

+pub mod simple_gen;
+pub mod simple_ir;
+
+pub use crate::simple_gen::*;
+pub use crate::simple_ir::*;