operators now only look ahead for whitespace after
 - `parenIsForExp` no longer needed for operators
Change the definition of op so that it appends (?=\\s) instead of (?=\\s+)
When looking ahead for just one suffices.
Caret is now an op, put with the other ops (moved over disjoint regexps)
Look ahead for trailing whitespace with more tokens (see table below)

              | check + match  | have
              | trailing space | `parenIsForExp` set
--------------+----------------+--------------------
`COMMA`       |                |        X
`THINARROW`   |                |
`THICKARROW`  |       X        |        X
`COLONCOLON`  |       X        |
`COLON`       |                |        X
`EQUALS`      |                |        X
`COLONEQUALS` |                |        X
`SEMI`        |       X        |        X

Conflicts:
	src/js/base/pyret-tokenizer.js