Unifying dataflow analysis.

See Middleend.FlowGraph.Analysis for impl.

Dataflow analysis can be divided into two flavors: forward analysis and
backward analysis. Bwd analyis is implemented but it seems buggy and I'm
going to look at it for a while...
Bug fixed by monadic right-to-left map.

Liveness analysis based on the new generic flow analyzer should be working
fine now.

BTW, I think Data.Traversable should add a mapRM...
Bug fix in block retracer and many more.

It should sufficient to create traces of flowgraphs now.

Besides...

- %rax is added as a use in X64.CALL when it's a vararg call.
- Added an asm("%reg") construct to retrive the current register value.
More loop construct: continue/break added

...First time to use RWST, I think it is extremely powerful since it models
exactly how imperative language users would like to write code. Amazing.