Add a basic regular expression engine to the dictiter, and to the UI add
the ability to filter for "starts with", "contains" and "ends with",
which translate into ANDed RE_*, _*RE_* and _*RE, respectively (with
_ standing for blank/wildcard). The engine's tightly integrated with the
next/prevWord() functions for greatest possible speed, but unless
there's no pattern does slow things down a bit (especially when "ENDS
WITH" is used.) The full engine is not exposed (users can't provide raw
REs), and while the parser will accept nesting (e.g. ([AB]_*[CD]){2,5}
to mean words from 2-5 tiles long starting with A or B and ending with C
or D) the engine can't handle it. Which is why filtering for word length
is handled separately from REs (but also tightly integrated.)
Users can enter strings that don't map to tiles. They now get an
error. It made sense for the error alert to have a "Show tiles"
button, so there's now a dialog listing all the tiles in a wordlist,
something the browser has needed all along.
