Checking in changes prior to tagging of version 0.19.

Changelog diff is:

diff --git a/Changes b/Changes
index 2bcc004..d7254f5 100644
--- a/Changes
+++ b/Changes
@@ -1,5 +1,8 @@
 Revision history for Algorithm::HyperLogLog

+0.19    Mon Jun 17 22:30:00 2013
+        - Change MurmurHash3 implementation for PP
+
 0.18    Sun Jun 16 23:50:00 2013
         - Update dependency
         - Change document format