Reorganization, global code motion, backward dataflow, loop tree construction, dom tree improvements, collapse region chains in CCP

CCP, DCE, GVN, IR Builder API, improve verification, rewrite dot visualization

See merge request !6

Fix dominator based verification, add structural checks

See merge request !5

Verify dominance relations in IR graph

See merge request !4

Dominators + post-dominators, subgraphs, thread ID + collect nodes, document IR

See merge request !3

Def use, dataflow, typechecking, structural verification, IR and DESIGN.md updates

See merge request !2

Finish core IR definition, parsing, and write to .dot graph

See merge request !1