licenses: convert license tags to SPDX

lib: improve wp tracing

When tracing wp can now print the instantiated version of the rules being used.
It also says which set each used rule is from.

lib: improve message printing for crunch and wp, and refactor common printing functions

lib: wp cleanup and parser improvements

The main visible change is from wp_trace', 'wp_once' and 'wp_once_trace' to
'wp (trace)', 'wp (once)' and 'wp (once, trace)'. The option for printing a
warning for unused supplied wp rules has also been removed.

lib: Datatype_Schematic and WPFix.

Add two new tactics/methods which can fix common painful problems with
schematic variables.

Method datatype_schem improves unification outcomes, by making judicious use of
selectors like fst/snd/the/hd to bring variables into scope, and also using a
wrapper to avoid singleton constants like True being captured needlessly by
unification.

Method wpfix uses strengthen machinery to instantiate rogue postcondition
schematics to True and to split precondition schematics that are shared across
different sites.

lib/wp: Slight cleanup in WP-method.ML

Removes all trailing whitespaces

wp: separate wp_pre method, used in wp and wpc

apply_debug: discard context modifications

Demotes "break" to a regular tactic, simplifying its integration with other tools

apply_debug: support context modifications in wp

Rebuild the ruleset if the context changes during execution.
This allows breakpoints to modify the wp set (during a given execution),
although this does not survive outside of the method.

apply_debug: add "wp" breakpoint

Lift low-level wp tactic into context_tactic to support
breakpoints modifying context (i.e. wp set)

wp: more constrained behaviour

- restrict to one goal (no fall-through)
- apply a wp_pre rule if there is no schematic in the goal
- apply trivial cleanup rules at the end

autolevity: refine tracing apply everywhere to work via Proof module hooks

This avoids doing redundant tactic operations at the top-level and lets
us trace "by" statements easily.

lib: start disentangling spaghetti word dependencies