Some further cleanup and 1.13 cherry-picks

Are most of these changes small and petty? Yes. However, IMO they do
make the code more readable. Anyway, a summary of some of the more
interesting changes:

 - Expose Abstract*Upgrade classes in the API
 - Fix the spelling of Jonathan in the API docs (*shakes fist*)
 - Fix bug with printout not working in the offhand.
 - Rename any argments/variables accidentally named "m_*", and add an
   inspection to prevent it happening again.
 - Remove most of the Block*.Properties classes - just inline them in
   the parent class.
 - Return super.writeToNBT instead of reassigning at the top.

tools/language.lua

@@ -74,7 +74,7 @@ for _, language in ipairs(secondary) do
     end
 
     local h = io.open(path:format(language), "wb")
-    local previous_blank = flase
+    local previous_blank = true
     for _, line in ipairs(primary_contents) do
         if line == "" then
             if not previous_blank then