expand_list to interactively work on a list of subgoals

also Tactical.VALID_LT, to check that a list-tactical is valid
(expand_list checks validity, expand_listf doesn't)

also abbreviations elt, eall, eta, enth to apply (list-)tactic to subgoal(s)
Add assembly code entry points for some decompiler tools.
Add a verified balanced binary tree example

This is based on the implementation of weight balanced binary search
trees in the ghc Haskell compiler's standard library.

comparisonScript.sml has a basic theory of comparisons that return
either Less, Greater, or Equal. This is not compatible with the existing
totoScript.sml, because I don't require cmp x y = Equal ==> x = y, but
it does.

osetScript.sml uses the balanced trees to implement sets.

Functional correctenss of the operations is verified, along with the
balancing properties.
VALIDATE and VALIDATE_LT

If tac (ltac) is invalid due to proving theorems with extra assumptions,
VALIDATE tac and VALIDATE_LT ltac  make the tactic valid by returning extra
subgoals to prove the extra assumptions
Add balanced_bst to build sequence at selftest level 2.
Add deep_matches to build sequence at level 1.
Mention balanced_bst example in release notes.
Merge pull request #216 from jeremydaw/expand

expand_list to interactively work on a list of subgoals