Add a synthetic changelog

CHANGES.md

+0.1.1 (2014-02-13)
+==================
+
+ * New subcommands in belenios-tool: "mkelection" and "election vote"
+ * Add a demo (bash) script to simulate a whole election
+ * Prettier URLs for election pseudo-files
+ * Fix compatibility with reverse-proxies
+
+0.1 (2014-01-13)
+================
+
+ * First public release