all: remove theory import path references

In Isabelle2020, when isabelle jedit is started without a session
context, e.g. `isabelle jedit -l ASpec`, theory imports with path
references cause the isabelle process to hang.

Since sessions now declare directories, Isabelle can find those files
without path reference and we therefore remove all such path references
from import statements. With this, `jedit` and `build` should work with
and without explicit session context as before.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

licenses: convert license tags to SPDX

lib: various crunch improvements

The main one is that crunch now uses wpsimp when determining whether a goal
can already be solved, instead of just wp. Crunch can also now use wps
when proving a goal and will now always ignore a constant if told to, even
if it is the top-level constant being crunched.

global: isabelle update_cartouches

lib: clean up BCorres_UL

lib: Refactor crunch so that it can be used for both the nondet monad and the trace monad

Removes all trailing whitespaces

wp_cleanup: update proofs for new wp behaviour

The things that usually go wrong:
- wp fall through: add +, e.g.
apply (wp select_wp) -> apply (wp select_wp)+

- precondition: you can remove most hoare_pre, but wpc still needs it, and
sometimes the wp instance relies on being able to fit a rule to the
current non-schematic precondition. In that case, use "including no_pre"
to switch off the automatic hoare_pre application.

- very rarely there is a schematic postcondition that interferes with the
new trivial cleanup rules, because the rest of the script assumes some
specific state afterwards (shouldn't happen in a reasonable proof, but
not all proofs are reasonable..). In that case, (wp_once ...)+ should
emulate the old behaviour precisely.

Refactor of crunch.

Substantial adjustments to crunch. Main user changes are:
- 'lift' and 'unfold' mechanisms replaced by more general 'rule'.
- some more 'ignores' standardised.
- crunch has a more principled overall design:
+ discover crunch rule
* provided or by definition extraction
+ recurse according to rule
+ prove goal based on rule, recursive discoveries, standard tactic
* wp/simp adjustments tweak tactic

lib: start disentangling spaghetti word dependencies

Proof updates, working as far as AInvs.

comment cleanup

Import release snapshot.