Add retries to requests

[landgraf]

Client retries if timeouterror/socketerror is raised for better reliability and workaround networking problems

[landgraf]

As was mentioned before the main purpose was to use sleeps not only retries as more reliable sleep renamed to backof

[david-caro]

Sorry, but I did not see that mentioned anywhere. Btw. I'm not sure I understand that last sentence, I'd be grateful if you rephrase.

If you need to tweak so much the behavior of the retry, I suggest two modifications:

• Explicitly depend on urllib3, instead of relying on the internal import of requests (it might change without notice) import directly from urllib3, and explicitly require it in the requires.
• Use parameters and default values instead of globals, that will allow you to tweak the values without having to modify the lib code or monkey-patch it.