Fixed silly compile error referring to a removed namespace.
Decoding ASCII in UTF-8 no longer needlessly increments a local pointer.
Bashed superfluous comment.
UTF-8 updates.

- Added public decls for objects in namespace Utf8. They're useful to clients, though more care must be taken to use them safely.
- Changed the return value of Decode back to bool, and the result is returned through a param. The slowdown is < 1%, and now clients can distinguish between decoding 0xFFFD and decoding failing.
- Doc updates. Bashed stale Decode() docs.