Enable streamable utf8 <--> utf16 codec

[manojampalam]

A fundamental issue exists on the Unicode data transition boundary, when the data travels as a stream.

This may manifest as ssh remote sessions breaking down with rare and random failures/aborts.
Ex. #767
To decode a Utf8 stream to Utf16 and vice versa, we need a stateful parser that accounts for partial input. The current implementation (that is a simple wrapper on MultiByteToWideChar), simply fails when fed with partial input.