Import initialization methods from the C++ API

[ccouzens]

We should import initialization methods from the C++ API.

There are functional features only available this way.

antimatter15/tesseract-rs#28

Whilst we mostly use the C API, we currently import a couple constants from the C++ API. See this PR for the code that currently imports from a C++ header:

antimatter15/tesseract-rs#9

[nico-abram]

I haven't been able to find a rust-bindgen example for a C++ method that takes a std::vector<std::string>. It sounds like it might be quite a problem because of inline methods on those std types. I found a recommendation in this rust-bindgen issue rust-lang/rust-bindgen#738 (comment) to use the cxx crate instead, but that seems like a pretty big addition/change to tesseract-sys