Register functions, properties and signals snake case

[chippmann]

Resolves #141

[raniejade]

Also we probably need a specialized extension for callDeferred.

inline fun <reified T: KFunction<*>> Object.callDeferred(method: T, vararg args: Any?) {
    callDeferred(method.name, args)
}

class S : Node() {

    @RegisterFunction
    override fun _ready() {
        callDeferred(this::fooBar)
    }

    @RegisterFunction
    fun fooBar() {

    }
}