Web Server Improvements

[efrecon]

This PR focuses on 3 things (sorry!):

• It fixes issue Unable to host under subpath  #39 by passing directly the configured root path.
• It adds access logging to the serve sub-command. All accesses, including errors, are logged through logrus at the info (success), or warn (error) levels. Lines provide information about the requests/response from the server. Logging is on by default, and can be turned on using the --log flag at the command-line.
• It uses dynamic information from the github context when building and testing in the GitHub workflows. This facilitates for forks to properly run the workflows, as the resulting packages will be hosted within the fork's account.

Docker images corresponding to the content of this PR can be found within my fork

[efrecon]

A side note, as this was mentioned in the original issue: I have tested this behind the Caddy v2 reverse proxy. Pointing to it with the handle directive performs as expected. Provided shiori is run with --webroot /shiori/. The following configuration snippet is all that is needed:

  redir /shiori /shiori/
  handle /shiori/* {
    reverse_proxy http://shiori:8080 {
    }
  }

[fmartingr]

Awesome @efrecon, I think we're good to go!

Thanks a lot for your improvements :)