forminfo.go:
- Wrappers for table data.
- Per Form dispatch table.
composition.go:
- reorderBuffer type.  Implements decomposition, reordering, and composition.
- Note: decompose and decomposeString fields in formInfo could be replaced by
  a pointer to the trie for the respective form.  The proposed design makes
  testing easier, though.
normalization.go:
- Temporarily added panic("not implemented") methods to make the tests run.
  These will be removed again with the next CL, which will introduce the
  implementation.

R=r, rogpeppe, mpvl, rsc
CC=golang-dev
https://golang.org/cl/4875043