Added a fast subroutine to multiply two signed 8-bit numbers.
Fixed the comments to say where the actual Left-Hand Side and Right-Hand Side are put.

A description of positions [left, right] is appropriate more for C code than for Assembly code.  (A description of timing [first argument, second argument] is more appropriate for the way that Assembly code is written.)
Merge pull request #115 from greg-king5/cc65-mul

Add a signed 8-bit times 8-bit multiply function.