Unified Provider model; existing DNS providers to be converted piecem…

[mmaney]

…eal.

Never used http_providers and shim removed; use unified interface for http-01.
Began removal of the torturous import of import chains; remainder are deprecated.
Test cases that no longer apply removed; others updated to match changes.

notes

This has, I think, the best of the various lines of work that I now think of as 0.9, which will be a release with more disruptive changes I have tried to keep the changes visible to users of both cli and the Client class to a minimum. The latter have had some unavoidable changes to implement the updated protocol cleanly, though if you're using Client through one of the high level interfaces (cert, renew, or get_certificate which the first two are aliases for) I think you'll find it mostly unchanged. The only change in cli.py, aside from adding two new providers, was the cleanup of logging back in #173.

There may be a few other minor changes or cleanups, and I definitely have some work to do on documentation, especially of what changed here. In preparing this I removed some very long and tedious comments from, especially, the new ProviderBase class which will become docs/provider.md (or some such, since I find that all writing, not excluding code, can be prone to finding its own shape as one gets it down on paper. refactoring is just our cult jargon for revising a draft, after all!).

[codecov]

Codecov Report

Merging #178 into master will decrease coverage by 0.08%.
The diff coverage is 89.84%.

@@            Coverage Diff             @@
##           master     #178      +/-   ##
==========================================
- Coverage   86.23%   86.15%   -0.09%     
==========================================
  Files          19       18       -1     
  Lines        1090     1141      +51     
==========================================
+ Hits          940      983      +43     
- Misses        150      158       +8     

Impacted Files	Coverage Δ
sewer/auth.py	83.33% <82.97%> (ø)
sewer/dns_providers/powerdns.py	93.33% <85.71%> (ø)
sewer/dns_providers/common.py	96.00% <94.11%> (-4.00%)	⬇️
sewer/client.py	89.16% <94.64%> (-0.17%)	⬇️
sewer/__version__.py	100.00% <100.00%> (ø)

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[komuw]

Here is an overview of what got changed by this pull request:

Issues
======
+ Solved 1
- Added 1
           

Complexity increasing per file
==============================
- sewer/providers/demo.py  3
- sewer/tests/test_auth.py  3
- sewer/providers/tests/test_demo.py  3
         

Clones removed
==============
+ sewer/tests/test_Client.py  -7
         

See the complete overview on Codacy