Add retries and timeout options to API calls

Add to all the API calls the `retries` and `timeout` options to manage the error responses. Consider a `retry-wait` option to manage retry speed.

`retries` - number of times to try the request before failing (default=1)
`timeout` - time to wait before interpreting the request as failed
`retry-wait` - the base time to wait between tries for exponential backoff

Note: `retries` should probably be `tries` but the parameter name retries is in too wide use to fight against.

It would be useful if these options were added to GhApi as defaults for all API calls made.