Card description / name re-writes.

 * Updates to a bunch of effect descriptions, some to be more specific
   about potential new effects, and removing the concept of "you" to
   instead substituting in "user".
 * Re-arrange the file to roughly group per-base-deck-concept, with
   priority in placement granted to the order of base decks in decks.cc.
 * Actual lines of what the cards depict! Mostly a whole bunch of
   vaguely-symbolic vaguely-iconic flavour, but it should be a nice touch
   if anybody actually looks up cards on ?/c (which they should, since
   there are so many changes upcoming.)
   Thanks to nicolae-, PleasingFungus, ontoclasm, and the rest of
   ##crawl-dev for producing the majority of these lines.
 * Better / more consistent summarizing comments on the card listing
   in decks.h, just in case anybody reads that.