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Update sample config to clarify that - needs quotes around it

Fixes https://github.com/turt2live/matrix-media-repo/issues/215

Fixes https://github.com/turt2live/matrix-media-repo/issues/214

I really need to get into the habit of doing this.

See d0c83eb4

We'd return a 500 when the token isn't found on the homeserver, but we should be returned a proper auth error. This just fixes the logic around the area to make that actually work.

If we use the request context, by the time we get a chance to do anything it will have been cancelled. We should be setting a new context so we can control its cancellation. 

The script appears to work, just needed some touchups.

Fixes https://github.com/turt2live/matrix-media-repo/issues/93

The coverage is handled by Circle CI and AppVeyor

Fixes https://github.com/turt2live/matrix-media-repo/issues/39

Fixes https://github.com/turt2live/matrix-media-repo/issues/63