rave: Add virtual file system module.

The rave virtual file system allows a user to transparently mount various
file sources like a real file system, archives and even HTTP sources uniformly
on a virtual file tree.

Files are provided by so-called providers, of which three variants exist:
- Mounts: regular sources of files. These will be mounted at a certain path in
  the file system and will provide files like usual.
- Transformers: these will take existing files and transform them into a new set
  of files. An example would be a transformer for a ZIP archive that unpacks the archive
  in-filesystem.
- On-demands: like mounts, these are sources of files, but they only answer specific
  inquiries. They have no way to list files and are not explicitly mounted on the file
  system. An example would be a provider that provides files over HTTP(S).
build: Add basic infrastructure and configuration files.

This adds the basic setup metadata stuff and continous integration
configuration files. rave uses nose to run tests, and its coverage.py
plugin to generate coverage reports. Moreover, for now we'll try to see
if a simple setuptools.py can do for us, before we have to switch to
anything more complex.
misc: Update LICENSE authors.
tests: Add filesystem module tests.

These should test every relevant aspect of the filesystem module.