Allow for multiple speakers

[marc-bouvier]

Sometimes there are several people talking during a keynote.

In the following example Rebecca Parsons is not visible until you read the description of the video.
https://dev.tube/video/-4fA_UciDaA

[sizovs]

@marc-bouvier Finally we added support for multiple speakers.

speaker:
    - name: Martin Fowler
      twitter: martinfowler
    - name: Rebecca Parsons
      twitter: rebeccaparsons

[marc-bouvier]

@sizovs Awesome!