Added links to GitHub repo and issue tracker.

This will display "Bug tracker" and "Source repository" fields
on Hackage in order to facilitate access to these resources.
See http://hackage.haskell.org/package/base for an example.

hakyll.cabal

@@ -8,6 +8,7 @@ Description:
 Author:         Jasper Van der Jeugt
 Maintainer:     jaspervdj@gmail.com
 Homepage:       http://jaspervdj.be/hakyll
+Bug-Reports:    http://github.com/jaspervdj/Hakyll/issues
 License:        BSD3
 License-File:   LICENSE
 Category:       Text
@@ -15,6 +16,10 @@ Cabal-Version:  >= 1.2
 
 build-type:     Simple
 
+source-repository head
+  type: git
+  location: git://github.com/jaspervdj/Hakyll.git
+
 library
   ghc-options: -Wall
   hs-source-dirs: src/