added !GUARD pattern (untested)
basic nt started
... converting to nts
... updated block rep
... nts working!

Still need to do:
 - update tactics impl (?)
 - update existing tactics to use new pattern syntax
 - update readme
... fixed lots of bugs
... example of computed pre-output
... simplify sexprw-template use
... generalized nt clause handling, added :with
... more conversion, more bug fixes
... finished updating racket-rewrites to nts
fix bugs in rect kill/yank, add collapse-space
made sexprw-template return 'pre entry
introduce and use !SL (soft newline)
changed tactic rep, impl
finish converting racket tactics
update version, comments
fix bug in sexp parsing
move undefined-nt check
added elisp vector stx, [], as sugar for !SQ pattern/template