changed repl prompt

changed repl prompt

commented out failed attempt at providing 'for X in [1,2,3]'

hid developer tools from repl.

trace:

  - fixed cycle detection

  - terser information printed for each edge.

    item => value

      | += val1
      |
      |    instantiated rule with subexpressions and variable values shown
      |    inline.
      |
      |     RECURSE on items in rule.
      |
      | += val2

  - changed color coding.

  - documentation, `> help trace`

No more barfing on empty input to trace, query, vquery.