Log Message:
Update to 0.18

Release notes:
## Version 0.18 (June 5, 2013)

_New features_
  - All extra argument monitors taking a string (e.g. `-O` for
    `BatteryP`) accept now template variables (see [github #109] and
    [#110]).  Thanks to Todd Lunter.
  - New battery monitor extra argument, `-i`, for the idle status.

_Bug fixes_
  - Safer standard input parsing, avoiding <action> injections.

[github #109]: https://github.com/jaor/xmobar/issues/109
[#110]: https://github.com/jaor/xmobar/issues/110