Introduced the class definition outside, added assertion that only one instruction is needed for processing iname_duplication_with_deps and some doc improvements.

Done some major changes in `iname_duplication_with_deps`, so that it gives out correct transformation

Got started with checking whether an option needs expensive duplication. Need something equivalent to `node.free_indices`

Use none for unknown dtypes

See merge request !200

Set target on dtypes in type inf

See merge request inducer/loopy!199

Fix arg inference for predicates (closes #114).

Closes #114

See merge request !198

add codepy caching test

Closes #113

See merge request !196

C exec cleanup

See merge request inducer/loopy!195