tools: update_changelog.sh and entire ChangeLog.

tools/update_changelog.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+FILE="$(dirname "$0")/../ChangeLog"
+UPDATECMD="git log --oneline --decorate"
+
+echo "Updated on `date`." > $FILE
+echo "If working with git, use \`$UDATECMD\` for latest change log." >> $FILE
+echo "------------------------------------------------------------------------" >> $FILE
+$UPDATECMD >> $FILE