Add CHANGELOG file

This patch adds a changelog file to reflect version changes history.

CHANGELOG.rst

@@ -0,0 +1,20 @@
+Changelog
+=========
+
+1.1.0 (unreleased)
+------------------
+
+**Features:**
+
+- Add base log path option: `-b` `--log-base`.
+- Log postfix option: `-p` `--log-postfix`.
+- Auto alias generation: `-a` `--alias-level`.
+
+**Bugfixes:**
+
+- #13: timestamp output adding 000 to microseconds.
+
+1.0.3 (2015-11-08)
+------------------
+
+- Initial release as os-log-merger.