Do not require dependency-injecting broccoli

The Filter base class that we are using is a helper, and has very
limited interaction with Broccoli core. So it is OK if we have
mismatching Broccoli versions. In the future, Filter will likely be
extracted into a separate package.
Use cute constructor-without-new pattern

https://twitter.com/jo_liss/status/431887815644045313
Release version 0.0.4