language specification
Honestly, what is really missing is how to use the different modules and what is the general data flow. I digged through the source and now got an impression how I can make use of it, but starting with a simple "how to install" down to what component uses which for what reason would be really helpful.
I really like your design and found planned future extension points (e.g. ModuleLoader). What's really fantastic is how easy modules (either as source or native) could be added.
You should also promote stdlib/func_typedefs.go a little bit more since it makes it super convenient to use for adding additional native modules and custom functions.