Closes: #86

As Pierre pointed out in [MR187](RT-PROOFS/rt-proofs!187),
we don't want updates in any of our dependencies to accidentally
shadow Prosa symbols. Hence, always import Prosa modules last to make
sure Prosa symbols "win" any name clashes.

* use more concise name
* add cases with [is_true _] in addition to cases with [_ = true]

Fix a typo and note Pierre Roux's comment on disjuctions vs inductives.

See also: #54 (comment 42229)

While at it, clean up some Markdown rendering issues on Gitlab.

This partially addresses #54.

- 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

Obviously incomplete, but a start.

First housekeeping steps...