polyhedral: AST gen: improve code intelligibility
polyhedral: AST gen: more readability improvements
polyhedral: model generator: fix a couple bugs

* fix slicing
* copy stream_view before updating access pattern

* remaining issue: introducing a memory leak:
  we don't know when we can delete previous stream_view,
  i.e. when it is not shared anymore.
polyhedral: use CLooG for AST generation
polyhedral: reduce debug output
prototype translator from ClooG AST to LLVM IR

Missing: actual translation of polyhedral statements.