Engine C/C++ external APIs should convert to UTF-8

[isc-woodfin]

iknow/modules/iknowpy/engine.pxd

Line 30 in 60b1c74

ctypedef unsigned short Entity_Ref

This line suggests the engine API is exposing our internal UTF-16 string representation. Though cognizant of the performance hit, I think we need an API where all string content is ordinary char*'s of UTF-8 (maybe not the only one, but certainly the one that code like @adang1345's would use)

[JosDenysGitHub]

We refer to literals via offsets in the text (and not making a copy as we used to do), that text is supposed to be of a fixed character size (UCS-2), if we convert to (multibye) utf8, we should also convert to byte offset.
Python also used UCS-2 as it's internal text representation, for all string - offset combinations to work in more exotic languages. But for emitting tracing strings, that surely can be utf8 encoded.