use setup.py requirements in requirements.txt

Instead of duplicating the requirements use the ones from setup.py. Also,
change the required versions of the libraries.

Signed-off-by: Michael Walle <michael.walle@kontron.com>
move library code to library.py

Just import the library in __init__.py. Also import the __version__ in
__init__.py, if it is available.

Signed-off-by: Michael Walle <michael.walle@kontron.com>
remote requirements.txt

Use "setup.py develop" for travis CI instead.

Signed-off-by: Michael Walle <michael.walle@kontron.com>