python: Update metainformation to point to new URL and version number

Convert the meta information to point to the notmuchmail.org repository, rather
than the old cnotmuch location. I will delete the "cnotmuch" package
from http://pypi.python.org/pypi/cnotmuch and create a new "notmuch"
package there that contains the current versions.

Also bump the version number to 0.4. I will need to upgrade the API
first before I can release the 0.5 of the bindings, there are still some
methods missing.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>