[docs] add docs for errback

Author: pawelmhm

docs/source/api.rst

@@ -96,9 +96,16 @@ callback
     - type: string
     - optional
 
-    Should exist as method of scheduled spider, does not need to contain self.
+    Must exist as method of scheduled spider, does not need to contain string "self".
     If not passed or not found on spider default callback `parse`_ will be used.
 
+errback
+    - type: string
+    - optional
+
+    Scrapy errback for request made from spider. It must exist as method of
+    scheduled spider, otherwise exception will be raised. String does not need to contain 'self'.
+
 max_requests
     - type: integer
     - optional

docs/source/conf.py

@@ -55,9 +55,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '0.10'
+version = '0.12'
 # The full version, including alpha/beta/rc tags.
-release = '0.10'
+release = '0.12'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.