exp/norm: added trie lookup code and associated tests.

- triegen.go: Factored out trie generation code from maketables.go
  (only renamed printTrieTables to printTables and made it a method).
- maketesttables.go: new tool to generate data for the trie unit test.
- Makefile: changed accordingly.
- trie.go: trie lookup code.
- trietest_data.go: generated by maketesttables.go.
- trie_test.go: unit test for trie.go.

R=r
CC=golang-dev
https://golang.org/cl/4844053