gh 1.4.0

• gh() gains a new .max_rate parameter that sets the maximum number of
  requests per second.

• gh is now powered by httr2. This should generally have little impact on normal
  operation but if a request fails, you can use httr2::last_response() and
  httr2::last_request() to debug.

• gh() gains a new .max_wait argument which gives the maximum number of
  minutes to wait if you are rate limited (#67).

• New gh_rate_limits() function reports on all rate limits for the active
  user.

• gh can now validate GitHub fine-grained personal access tokens (@jvstein, #171).