SwitchBlade1 was a rudimentary encoder that only did I frames.

SwitchBlade2 was a near-total rewrite and did P frames correctly.

SwitchBlade3 is based on just about the same methods as SwitchBlade2
(STDVQ codebook generators, three-step motion searching, list-sort
progressive reductionrate control), but is mostly a rewrite.

- Only reused code is the STDVQ generator
- More accurate YUV calculator
- Reducer knows the codebook chunk size, making rate control MUCH
  more accurate.
- Replaced floating-point scaling checks with simple integer
  fraction comparisons, which are faster and more reliable.
- Library is now 100% integer-based and thread-safe.
- Source code is a lot cleaner.

Currently, SwitchBlade3 does *NOT* support thresholding like
SwitchBlade2.  Whether that feature will be re-added is currently
being debated.