Refactoring

-   Put everything in `src` directory
-   Put all tests under the `observer` package
-   Rewrite runtests.py
-   Rewrite setup.py
-   Rewrite and improve tests
-   Improve django compatibilities (Django 1.3-1.6)
-   Improve python compatibilities (Python 2.6-3.3)
-   Introduce tox, coverage, coverall, travis
-   Split utility functions into observer.utils
-   Split shortcut functions into observer.shortcuts
-   Simplify watchers
-   Improve compativility
    -   Python 2.6-2.7
    -   Python 3.2-3.3
    -   Django 1.2-1.6
-   Improve unittests
-   Add generic manage.py