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.

lib: improve the parser for crunch.

The main benefit of this is that everything in crunch is now ctrl clickable.
As an added benefit, supplied rules can now be modified by attributes when
needed.

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

lib: Add multi-crunch command 'crunches'.

It's just a parser tweak for crunch, and runs multiple crunch commands
with the same sections (wps, ignores, etc).

Also update the comments a little, and move them closer to the anchor of
command clicks (the @{command_keyword} antiquotation).

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

arch_split: added optional definition override for crunch. Reduced qualification commands to minimal required set.

Import release snapshot.