Reorder the TODO notes in fastdupes.py to roughly approximate priority.
Unify and debug the use of \r in fastdupes status messages.
If limit is less than chunk_size in fastdupes.hashFile, obey the former.
Add a TODO note to fastdupes about finding a smaller HEAD_SIZE value.

(64K is definitely more than necessary and dropping it to 32K knocks 25%
 off the WARM-cache runtime.)
For now, use 16KiB as the value for HEAD_SIZE to optimize things more.

(It still has minimal false positives in the third phase but is
 significantly quicker in the second.)