add API functions to get list of resources names

With these new functions, it is now possible to get through the API the
list of domains, networks, storage volumes and storage pools as declared
in the YAML file.

Fixes #16.
ignore dirs created by setuptools in git
add MANIFEST.in file to include doc and tests

Sphinx doc and unit tests were missing of source distribution tarball
built by setuptools. This new MANIFEST.in file fixes it.
update installation instructions in documentation

The installation guide in the documentation now explains how to use
Cloubed Debian and Yum repositories.
Cloubed release v0.3
Merge remote-tracking branch 'upstream'
debian release 0.3-1