incremental comparisons. Instead, processing is now done directly on colElems.
As a result, the size of the weights array is now reduced by 75%.
Details:
- Primary value of type 1 colElem is shifted by 1 bit so that primaries
  of all types can be compared without shifting.
- Quaternary values are now stored in the colElem itself. This is possible
  as quaternary values other than 0 or maxQuaternary are only needed when other
  values are ignored.
- Simplified processWeights by removing cases that are needed for ICU but not
  for us (our CJK primary values fit in a single value).

R=r
CC=golang-dev
https://golang.org/cl/6817054