Sanic-cors

- New minimum supported sanic version is 18.12LTS
- Fixed bugs with Sanic 19.12
- Max supported sanic version for this release series is unknown for now.


_**Note**_, Sanic v19.12.0 (and 19.12.2) _do not_ work with Sanic-CORS 0.9.9 series or earlier.

This is the last version of sanic-cors to support Sanic 0.8.3
- Update to Sanic 18.12LTS (or higher) to use future Sanic-CORS releases

Bump Sanic-Plugins-Framework to 0.8.2.post1 to fix a big.
- This is also the last version of SPF to support Sanic 0.8.3

_**Note**_, Sanic v19.12.0 (and 19.12.2) _do not_ work with Sanic-CORS 0.9.9 series or earlier.
A new version coming out soon will work with sanic v19.12.

Revert previous patch. Sorry donjar

Apply fix for async error handlers. Thanks donjar

Actually fix import of headers on latest Sanic versions