This lists only the changes for the current release (v1.18) over the last
version, since HISTORY is now quite big:

# v1.16 was about 15% slower on (while $x++ < $e) loops. This version
  fixed binc() and bdec(), so that it is now about factor 4 faster. This means
  the loop above is now about twice as fast ;)
* as_number() is now about factor 2 faster

