Precompute find dependencies



See merge request !19

Implement multiple priority constaints in the scheduler

* Introduce prioritize_loops as a replacement for set_loop_priority
* Kernels now store a frozenset of such priority constraints
* The scheduler builds priority tiers taking all these into account
* Deprecate set_loop_priority

See merge request !14

Global barrier handling



See merge request !17

Fix temporary scope finding



See merge request !16

... no idea how my editor considered this a good idea.

Fix doctest for __restrict__



See merge request !15

in doc and tests.