Login/Token Creation

Allowing callers to create access tokens with valid user and client credentials.

```
client = PseudoCMS::API::Client.new(email: 'your@email.com', password: 'your_password')
token = client.create_token(
  client_id: 'YOUR_CLIENT_ID_HERE'
  client_secret: 'YOUR_CLIENT_SECRET_HERE'
)

token.access_token # the token
```

Currently this operation is only available via basic authentication