more docs and fixed bug in parser that assigned lineno for ExprStmt wrong

--HG--
branch : trunk
diff --git a/jinja2/parser.py b/jinja2/parser.py
index 8a0eb6a..8bc1307 100644
--- a/jinja2/parser.py
+++ b/jinja2/parser.py
@@ -52,7 +52,7 @@
             ext = self.extensions.get(self.stream.current.value)
             if ext is not None:
                 return ext(self)
-        lineno = self.stream.current
+        lineno = self.stream.current.lineno
         expr = self.parse_tuple()
         if self.stream.current.type == 'assign':
             result = self.parse_assign(expr)