NSEdoc cleanup

Mostly splitting function summaries (the first paragraph of NSEdoc) from
the body of the description to make the summary indexes shorter and
easier to scan.

Also fixed some unbalanced code tags like <code>foo</table>

nselib/json.lua

@@ -163,6 +163,7 @@ json = P(json); -- compile the grammar
 
 
 --- Parses JSON data into a Lua object.
+--
 -- This is the method you probably want to use if you use this library from a
 -- script.
 --@param data a json string