Fixed two operator lexing bugs
Fixed two operator lexing bugs

First, "0-a" should be tokenized to '0', '-', 'a' not '0-a'. Second,
it's legal to have whitespace between the binary & unary keywords and
the user operators that they are defining, so we must absorb that.

ripta/kaleidoscope,ripta/kaleidoscope,ajsnow/kaleidoscope,ajsnow/kaleidoscope