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).

- 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

- Removed unnecessary assumption in RTA about task precedence/no intra-task parallelism.
- Scheduler models and analyses are organized in separate modules/folders.
- Added RTA for FP and EDF for schedulers with release jitter.
- The scheduling invariants were split into more fine-grained assumptions:
  (a) scheduler is work-conserving
  (b) scheduler enforces FP/JLDP priority X
- New helper lemmas about counting, and sorted/uniq lists
- Inclusion of tactics feed and feed_n (see documentation).
- Added a Makefile generator