Try with make

I'm opening this PR for discussions.

This PR suggests replacing `zc.buildout` by `make`. By using `make` we gain a lot of flexibility. `zc.buldout` is good for Python projects, but is not that useful here. And by using `make` as done in this PR we can easily solve #14 (by installing the closure_linter in the venv created by the `Makefile`).

The `Makefile` is really easy to use. Here's the output of `make help`:

```
Usage: make <target>

Possible targets:

- css       Build CSS
- js        Build JavaScript
- deps      Build deps.js (for script autoload with Closure)
- index     Create index.html and index-prod.html
- lint      Run the linter
- test      Run the JavaScript tests
- all       All of the above
- clean     Remove generated files
- cleanall  Remove all the build artefacts
```