Python bindings: Make compatible with Python 3
Python bindings: Make compatible with Python 3

- replaced 'xrange' with 'range'
- Convert all strings to ASCII internally
- Remove use of filter()

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio