Integrate Fabulist into NovelRT

[FiniteReality]

After #383 we're currently stuck without any form of interface for non-programmers. We should implement Fabulist, our new VN language into NovelRT.

The idea is roughly:

• Fabulist is used to write VN contents
• Something else is used to store data for animations/scenes/etc (maybe Lua based too?)
• Something else is used to manage save states and such. (Fabulist will have a serializable "state" payload which represents the current state in the story, including things like variables)

[RubyNova]

I'm doing the basic integration, but once imgui is in this will still primarily be on @FiniteReality to ensure she's happy with the APIs etc.