wai-extra logging middleware should optionally log request before response is constructed

[sordina]

Waiting for the response before logging has issues:

• Exceptions can prevent logging
• Long response times delay seeing corresponding request logs

This makes using logging for development/debugging annoying and sometimes impossible.

Ideally the logging datastructures should be partitioned into request/response and middleware should be provided or be able to be configured to log the request as it arrives. For compatibility the full request/response information could still be logged once the response is generated if that makes sense.

Happy to put together a PR if people agree with this.

[snoyberg]

No objection from me, seems reasonable. PR welcome, though it should avoid breaking existing application behavior.

[sordina]

@snoyberg Something like this? #857

New logging output looks like:

PRELOGGING REQUEST: GET /favicon.ico
  Accept: */*
GET /favicon.ico
  Accept: */*
  Status: 404 Not Found 0.000098s

if option is enabled.