Allow sub-subclasses

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Readme move/update

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
s3 / boto support - updated drivers, tests, mock, etc etc

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Updated tests and requirements

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Trying at travis

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)