Nexmo

- Add new Voice API call methods

- Add Application API methods

- Add check_signature method for checking callback signatures

- Deprecate old Verify API methods

- Add get_sms_pricing method

- Add get_voice_pricing method

- Add get_event_alert_numbers method to get opt-in/opt-out numbers

- Add resubscribe_event_alert_number method to opt-in a number

- Add more clearly named methods for Verify API

- Add app_name and app_version options

- Add topup method

- Add update_settings method

- Add api_host attribute

- Add ClientError and ServerError classes

- Move repository to https://github.com/Nexmo/nexmo-python

- Add get_basic_number_insight method for Number Insight Basic API

- Add get_number_insight method for Number Insight Standard API

- Add User-Agent header to requests

- Change license from LGPL-3.0 to MIT

- Remove merge helper function