encodeUtf8_1: drop a loop induction variable

This helps performance quite a bit! Now encoding Japanese text is
2x faster than encodeUtf8, as opposed to 30% faster before. Not bad!
encodeUtf8_1: drop an unnecessary type signature

The value that was having too general a type inferred is now a
pointer, so inference doesn't accidentally overgeneralize.
Drop now-redundant imports
Export both encodeUtf8 variants
encodeUtf8_1: get my arithmetic right :-(
Begin 1.1 release notes