Check-iftraffic-nrpe

- add contributors in readme file
- Remove the "c" UOM of perfdata output. Closes 30

Features:
- add pnp4nagios template [Gavrilov Alexy]. Closes 28
- more unittests

Bugfixes:
- try to take care of malformed data file (eg: empty) Fixes 24
- use NagiosService.status() instead of non existent property. Fixes 27

- Python 3 support
- Add automated unit tests

- Nagios functions are now two Nagios classes
- More unit tests

Bump version lol

- Multiplier changed from 1024 to 1000 because this is network related
- command line option changes:
- New option `--unit` for more unit choices: [kMGT][bB](default: B)
- Option `--bandwith` must now be same unit as `--unit`
- Better code and code cleaning
- All functions are now commented
- PyLint proof
- DeviceError exception now uses super
- New style classes: now inherit from the "object" object.
- bits2bytes() is replaced by convert_bytes()
- reformatting of get_perfdata()
- More accurate diff calculcation
- More accurate Nagios status