Enable retries in the std.py backend.

[ShaheedHaque]

Resolves #30. This PR also:

• Replaces the deprecated call to requests.session() with its current counterpart, requests.Session().
• Allows arbitrary connection kwargs to be passed down, not least to allow the new retry behaviour to be overridden.

[codecov[bot]]

Codecov Report

Merging #31 (8622b26) into master (7aa1ff4) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
+ Coverage   94.45%   94.47%   +0.01%     
==========================================
  Files           6        6              
  Lines        1840     1846       +6     
==========================================
+ Hits         1738     1744       +6     
  Misses        102      102              

Flag	Coverage Δ
unittests	94.47% <100.00%> (+0.01%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
consul/std.py	100.00% <100.00%> (ø)

---

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 7aa1ff4...8622b26. Read the comment docs.

[ShaheedHaque]

Hi, is there any chance of a release with this PR incorporated? FWIW, there is a Celery fix (https://github.com/celery/celery/issues/5605) which benefits from this, and which I had wanted to delay before this was available but I feel I need to pursue at this time.

[ShaheedHaque]

@poppyred Any chance of a release with this merged please?