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

https://github.com/intersystems/iknow/blob/60b1c74224c29ae6a32bb9acac8677b1e7f58ef6/modules/iknowpy/engine.pxd#L30

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)