update README
Checking in changes prior to tagging of version 0.70.

Changelog diff is:

diff --git a/Changes b/Changes
index 551733a..f13e9a7 100644
--- a/Changes
+++ b/Changes
@@ -1,3 +1,8 @@
+0.70    Wed Aug 14 10:06:34 2013
+        - support float number
+        - support rrdcached for improve performance
+          (Thank you sonots)
+
 0.62    Fri Jun 28 11:37:55 2013
         - add more json api(Thanks sonots)
         - escape uri (Thanks sonots and shibayu36)