ACIP or 'ShSm' in Extended Wylie to see the new behavior.
We use a trie to store valid input sequences. In the future, we could use
the same trie as a replacement for the more inefficient HashSets we use to
store characters, vowels, and punctuation. For example, we'd use
'validInputSequences.put("K", new Pair("consonant", "k"))' when reading
in the ACIP keyboard's description of the first consonant of the Tibetan
alphabet in 'TibetanKeyboard.java'.
Note that the current trie implementation is only useful for 7- or 8-bit
transcription systems, and works best for tries with low average depth, which
describes a transcription system's trie very well. If you used arbitrary
Unicode in your keyboard, you'd need a different trie implementation.
Improved the optional keyboard input mode status messages.
