J2cli

* New: `env()` is now available as a function
* New: can now customize the `Environment` object
* Fixed documentation

* New: customize.py that lets you customize :)
* Fixed a bug with setup.py and yaml

* Enabled Jinja2 extensions: i18n, do, loopcontrols

* The new `{{ VAR_NAME |env }}` filter lets you use environment variables in every template.

* Fixed support for Python 2.6
* Dropped Python 2.6 from unit-tests~~~~
* Fixed a warning issued by PyYAML.
See [issue 33](https://github.com/kolypto/j2cli/issues/33)

* New option: `--undefined` that allows undefined variables
* Fix: unicode support in environment variables