existing data structure, and disturb as little of the existing code
as possible.
- So here's the tack. We add some caching to the scan_buffer
+ So here's the tack. We add some caching to the find_newline
function, so that when it searches for a newline, it notes that the
region between the start and end of the search contained no
newlines; then, the next time around, it consults this cache to see