Add pair_sms

Tidying up the language library. Matching functionality of toopher-python library. 
it would need to be either 

```ruby
  parameters.merge!(options)
  return PairingStatus.new(post('pairings/create/sms', parameters))
```
or 
```ruby
  return PairingStatus.new(post('pairings/create/sms', parameters.merge(options))
```