Add Script Handler signatures to API documentation

[Meorawr]

With 10.0 giving us the gift of automated API documentation for script object APIs, it'd be helpful if this were additionally extended to also document the signatures of script handlers such as OnHyperlinkEnter or OnTextChanged.

Currently, the only reliable way for us to determine what arguments are supplied to script handlers is through inspection of an debuglocals dump within a replaced global error handler.

As an example, given the following XML and Lua fragments we can use the debuglocals API to determine the names of the parameters generated for an OnHyperlinkEnter XML script handler chunk. While this will get us the magic names of parameters within generated XML script handlers, we can't automatically infer typing information for the individual parameters.

<Frame name="TestFrame">
    <Scripts>
        <OnHyperlinkEnter>error()</OnHyperlinkEnter>
    </Scripts>
</Frame>

local eh = geterrorhandler()
seterrorhandler(function(e) print(debuglocals(4)) end)
securecall(TestFrame:GetScript("OnHyperlinkEnter"))
seterrorhandler(eh)

This would output the following:

self = nil
link = nil
text = nil
region = nil
left = nil
bottom = nil
width = nil
height = nil