Add CHANGES file.

CHANGES

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+============================================================================
+User visible changes for btcd
+  A full-node bitcoin implementation written in Go
+============================================================================
+
+Changes in 0.3.1-alpha (Tue Oct 15 2013)
+  - Change default database to leveldb
+    NOTE: This does mean you will have to redownload the block chain.  Since we
+    are still in alpha, we didn't feel writing a converter was worth the time as
+    it would take away from more important issues at this stage
+  - Add a warning if there are multiple block chain databases of different types
+  - Fix issue with unexpected EOF in leveldb -- https://github.com/conformal/btcd/issues/18
+  - Fix issue preventing block 21066 on testnet -- https://github.com/conformal/btcchain/issues/1
+  - Fix issue preventing block 96464 on testnet -- https://github.com/conformal/btcscript/issues/1
+  - Optimize transaction lookups
+  - Correct a few cases of list removal that could result in improper cleanup
+    of no longer needed orphans
+  - Add functionality to increase ulimits on non-Windows platforms
+  - Add support for mempool command which allows remote peers to query the
+    transaction memory pool via the bitcoin protocol
+  - Clean up logging a bit
+  - Add a flag to disable checkpoints for developers
+  - Add a lot of useful debug logging such as message summaries
+  - Other minor bug fixes and general code cleanup
+
+Initial Release 0.3.0-alpha (Sat Oct 05 2013):
+  - Initial release