R1:b8bb4d3ad590

Accept either "[[ %24doge ]]" or "[[ $doge ]]" as references to the "/w/$doge/" Phriction document

Summary:
Depends on D19105. Ref T13077. Fixes T12344.

The `[[ ... ]]` syntax accepts and handles characters which would require URL encoding if they appeared in URIs. For example, `[[ 100% Natural Cheese Dust ]]` is a legitimate, supported piece of remarkup syntax, and does not need to be written as `... 100%25 Natural ...`.

Likewise, `[[ BUY $DOGE ]]` is legitimate and does not need to be written as `…