Fix issue #13

Detects when there are no JS file to minify

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Fix issue #14

The sass processor must track .scss and .sass files.

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Add some integration tests

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>