the need to decompose characters for the majority of cases.  This considerably
speeds up collation while increasing the table size minimally.

To detect non-normalized strings, rather than relying on exp/norm, the table
now includes CCC information. The inclusion of this information does not
increase table size.

DETAILS
 - Raw collation elements are now a struct that includes the CCC, rather
   than a slice of ints.
 - Builder now ensures that NFD and NFC counterparts are included in the table.
   This also fixes a bug for Korean which is responsible for most of the growth
   of the table size.
 - As there is no more normalization step, code should now handle both strings
   and byte slices as input. Introduced source type to facilitate this.

NOTES
 - This change does not handle normalization correctly entirely for contractions.
   This causes a few failures with the regtest. table_test.go contains a few
   uncommented tests that can be enabled once this is fixed.  The easiest is to
   fix this once we have the new norm.Iter.
 - Removed a test cases in table_test that covers cases that are now guaranteed
   to not exist.

R=rsc, mpvl
CC=golang-dev
https://golang.org/cl/6971044