Added positional offsets to each YangStatement

This allows the parse results to be used in applications like syntax highlighting / code
folding / etc.

src/yang-parser.litcoffee

@@ -221,12 +221,22 @@ The result of the `statement` parser is an initialized `YangStatement`
 object. If no argument is present, the object's `arg` property is set
 to `false`.
 
-    statement = keyword.bind (kw) ->
+    rawStatement = keyword.bind (kw) ->
       (sep.bind -> argument).option(false).bind (arg) ->
         strict = true if kw[1] is 'yang-version' and arg is '1.1'
         optSep.bind -> semiOrBlock.bind (sst) ->
           P.unit new YangStatement kw[0], kw[1], arg, sst
 
+    statement = new P (offset) ->
+      [stmt, end] = rawStatement.pf offset
+      
+      if stmt is null
+        [null, end]
+      else
+        stmt.sp = offset
+        stmt.ep = end
+        [stmt, end]    
+
 A statement block is a sequence of statements enclosed in
 braces. Whitespace or comments are permitted before or after any
 statement in the block.