add debug method to Rule.
Tweaks:

 - color REPL prompt leads to strange behavior because the width of the prompt
   appears to be miscalculated by readline.

 - tiny improvement to trace's output format

 - tiny tweak to codegen

 - doctest shows diff along with what was expected and what it got.
Interning is back! However, charts are never deleted.

Fix dict= aggregator, didn't handle the null.
minor refactor.
Many small tweaks.

 - fixed argument disposition of tupling operators: `->` and `:`.

 - Compare rules by their index (i.e. equality, hash,q and sort order).

 - Recompilation works like rule initialization
added crash summary.
ignore crashlog directory
Merge ../working