Ternary search trees added to TODO

[Russ Allbery]

Added to TODO, idea from some discussion on the gcc mailing list:

* INN currently uses hash tables to store the active file internally.  It
  should probably use ternary search trees instead; the data structure is
  simpler, performance is comparable or better for hits and significantly
  better for misses, sizing and resizing becomes a non-issue, and the
  space penalty isn't too bad.  For more information, see
  <http://www.ddj.com/articles/1998/9804/9804a/9804a.htm>.  A generic
  implementation in libinn may be usable in many places.

-- 
Russ Allbery (rra at stanford.edu)             <http://www.eyrie.org/~eagle/>