Add support for custom requests session (to support exponential backoffs)

[TimidRobot]

Issue

The requests session is currently hardcoded:

flickrapi/flickrapi/auth.py

Line 143 in c389ce9

session = requests.Session()

Potential Solution

Easiest change would be to allow the user to specify the session in FlickrAPI() and pass it to OAuthFlickrInterface.

The the user could configure exponential backoff themselves:

from requests.adapters import HTTPAdapter
from requests.packages.urllib3.util.retry import Retry

    # Requests configurations
    max_retries = Retry(
        # try again after 5, 10, 20, 40, 80 seconds
        # for specified HTTP status codes
        total=5,
        backoff_factor=10,
        status_forcelist=[403, 408, 429, 500, 502, 503, 504],
    )
    session = requests.Session()
    session.mount("https://", HTTPAdapter(max_retries=max_retries))

etc.

Additional context

• Advanced usage of Python requests - timeouts, retries, hooks
• Requests: HTTP for Humans™ — Requests documentation