Add RetryBackoff to support custom @retry backoff strategies

[prkumar]

Add a new base class, uplink.retry.RetryBackoff, which can be extended to implement custom backoff strategies. Subclasses can override three methods:

• get_timeout_after_response(request, response): Returns the number of seconds to wait before retrying the request, or None to indicate that the given response should be returned.
• get_timeout_after_exception(request, exc_type, exc_val, exc_tb): Returns the number of seconds to wait before retrying the request, or None to indicate that the given exception should be raised.
• handle_after_final_retry(): Handles any clean-up necessary following the final retry attempt.

An instance of a RetryBackoff subclass can be provided through the backoff argument of the @retry decorator.

#238

[codecov]

Codecov Report

Merging #247 (dee8883) into master (fc21923) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #247   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           44        44           
  Lines         2410      2466   +56     
  Branches       342       355   +13     
=========================================
+ Hits          2410      2466   +56     

Impacted Files	Coverage Δ
uplink/arguments.py	100.00% <100.00%> (ø)
uplink/auth.py	100.00% <100.00%> (ø)
uplink/commands.py	100.00% <100.00%> (ø)
uplink/compat.py	100.00% <100.00%> (ø)
uplink/converters/__init__.py	100.00% <100.00%> (ø)
uplink/converters/typing_.py	100.00% <100.00%> (ø)
uplink/decorators.py	100.00% <100.00%> (ø)
uplink/retry/__init__.py	100.00% <100.00%> (ø)
uplink/retry/backoff.py	100.00% <100.00%> (ø)
uplink/retry/retry.py	100.00% <100.00%> (ø)
... and 7 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e2f8225...dee8883. Read the comment docs.

[mivade]

Thanks!

[mivade]

@prkumar I really appreciate your quick work on this!