Introduced /key endpoint

We've introduced a new endpoint /key for conveniently monitoring your account's API usage, including rate limits and remaining credits.

Example of responses:

{
  "plan": "Other",
  "rate_limit_request_per_minute": 1000,
  "monthly_call_credit": 1000000,
  "current_total_monthly_calls": 307,
  "current_remaining_monthly_calls": 999693
}