A list of values for a parameter is obtained with a URL
such as &param=value1&param=value2
The returned dictionary will be:
{ param : [value1, value2]}

Update the build system to use pybuild.

The new binary package with Python 3 support is named
python3-cubicweb-elasticsearch according to current standards.
Python 2 package is also updated to use the proper namespace
and a transitional package has been introduced to handle
the migration.

Both packages depends on the python{,3}-elasticsearch-dsl,
currently available at:
https://salsa.debian.org/lunar/elasticsearch-dsl-py

Fix MANIFEST.in to include missing test files.

Support for Python 3.8 is disabled as it is currently broken
in Debian unstable.

The httplib module has been renamed to http.client in Python 3.
So let's try to import HTTPConnection from both.

- Fix errors:
  - TypeError: 'float' object cannot be interpreted as an integer

- Fix deprecation warnings:
  - DeprecationWarning: Please use assertEqual instead
  - DeprecationWarning: Please use assertTrue instead