Add changelog for 0.25.0.
Bump version to 0.25.0.

Changes:

* Add `environment` method to recipe to handle environment settings.
* Allow newer FPM versions than 1.1.
* Unbreak `configure` call without arguments on Ruby 1.8. (#92)
* Basic Scientific Linux support. (jjuarez / #93)
* Update internal recipes. (smasset / #89)