Preprocessor PCREs augmented.

Such PCREs now match a significant subset of valid here-document syntax, in
addition to the customary suspects (e.g., arithmetic and process
substitutions).

"The day is fleet,
 Flat-footed, and
 Bargainless. Unbrained
 Stem defray, that we may
 Stem waylayed tides of
 Ire on the islands' wist --
 Unmisted, unmentionable, and
 Mastless. Encroach away.

 A massless dark begets the
 Starkness of the
 Reaving's Day."