Implement CorsViewMixin

[pedrokiefer]

Fix #41!

[evandroeisinger]

Great contribution!

[codecov]

Codecov Report

Merging #145 into master will increase coverage by 3.55%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #145      +/-   ##
=========================================
+ Coverage   80.95%   84.5%   +3.55%     
=========================================
  Files           7       9       +2     
  Lines         357     413      +56     
  Branches       65      72       +7     
=========================================
+ Hits          289     349      +60     
+ Misses         44      42       -2     
+ Partials       24      22       -2

Impacted Files	Coverage Δ
aiohttp_cors/__init__.py	100% <100%> (ø)	⬆️
aiohttp_cors/cors_config.py	79.56% <100%> (-3.14%)	⬇️
aiohttp_cors/mixin.py	100% <100%> (ø)
aiohttp_cors/preflight_handler.py	100% <100%> (ø)
aiohttp_cors/urldispatcher_router_adapter.py	79.05% <100%> (+1.51%)	⬆️
aiohttp_cors/abc.py	100% <100%> (ø)	⬆️

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[asvetlov]

@pedrokiefer please take a look on https://codecov.io/gh/aio-libs/aiohttp-cors/pull/145/diff
Or install codecov browser extension to see test coverage just in github diff tab.
Yellow and red lines should be covered.

[asvetlov]

P.S. I like the PR in general, usage snippet looks pretty elegant.

[pedrokiefer]

@asvetlov thanks, i'll work on those issues tomorrow.

[asvetlov]

I see many duplications (copy-pastes from cors_config.py).
Would you refactor the code to avoid it?

[pedrokiefer]

My first try was reusing cors_config.py methods, and it failed miserably. Now that I've got a working version, with tests in place, might be easier to get it right.

Do you have any objection on extracting _preflight_handler, _parse_request_headers and _parse_request_method to another class, and composing both the mixin and _CorsConfigImpl ?

[asvetlov]

Do you have any objection on extracting _preflight_handler, _parse_request_headers and _parse_request_method to another class, and composing both the mixin and _CorsConfigImpl

Love the idea. Especially love underscore prefix for proposed names :)

[pedrokiefer]

Done! :)

[asvetlov]

Cool!
Let me make a final review and merge tomorrow.

[asvetlov]

Thanks!
Initiated 0.6.0 release