This commit contains several updates related to uniprocessor scheduling.

- Basic definitions of uniprocessor scheduling (see model/uni)
- Definitions of worload and service for generic sets of jobs (see service.v and workload.v in model/uni)
- Definitions and lemmas about busy intervals (see model/uni/basic/busy_interval.v)
- Definition of an arrival bound for sporadic tasks (see model/arrival_bounds.v)
- Definitions and correctness proofs of the RTA for FP scheduling
  (also works with non-unique priorities and arbitrary deadlines, but gives pessimistic bounds)
- Implementation of the FP RTA to check for contradictory assumptions

In addition, we have also defined partitioned scheduling and proven how it relates
with uniprocessor (see model/partitioned).

The BSD version of `find` needs to be given '.' as the search path.

- Add definitions related to APA scheduling
- Prove correctness of reduction-based RTA for APA scheduling (FP and EDF)
- Add implementation of a weak APA scheduler
- Update definition of taskset to assume uniqueness
- Modify names and comments to improve readability
- Remove strong assumptions about priority order in FP scheduling
- Add tests with FP RTA for every model
- Add tests for RTA with parallel jobs

We use simpler, more pessimistic interference bounds to
prove that Bertogna and Cirinei's RTA works for parallel jobs.