Update haskell98.cabal and add changelog

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

changelog.md

+# Changelog for [`haskell98` package](http://hackage.haskell.org/package/haskell98)
+
+## 2.0.0.3 *Mar 2014*
+
+  - Bundled with GHC 7.8.1
+
+  - Remove NHC98-specific code
+
+  - Adapt to changes in GHC 7.8's core-libaries
+
+  - Update to Cabal format 1.10

haskell98.cabal

@@ -14,8 +14,11 @@ description:
     This package provides compatibility with the modules of Haskell
     98 and the FFI addendum, by means of wrappers around modules from
     the base package (which in many cases have additional features).
-    However Prelude, Numeric and Foreign are provided directly by
-    the base package.
+    However "Prelude", "Numeric" and "Foreign" are provided directly by
+    the @base@ package.
+
+extra-source-files:
+    changelog.md
 
 source-repository head
     type:     git