Add script functions to get VivyDocument informations

Add a way to get more information about the VivyDocument in the scripting interface.

Depends on !21 (merged) for logging and some things changed in the LuaContext class (because of logging)

rsc/lua/lib.lua

@@ -83,6 +83,11 @@ function Vivy:newColor (colorString)
     return false
 end
 
+function Vivy:start  () return Vivy.___Fun:start()  end
+function Vivy:finish () return Vivy.___Fun:finish() end
+function Vivy:width  () return Vivy.___Fun:width()  end
+function Vivy:height () return Vivy.___Fun:height() end
+
 -- In case we are able to do the _ENV <- Vivy one day...
 Vivy["Vivy"] = Vivy