Add support for Flyspray

Support request for Rockbox, which uses Flyspray
http://www.rockbox.org/tracker/index.php?project=1&do=index&switch=1

Rockbox already uses GitHub for git mirror, might be easier to get them to switch issues to GH since we don't have any other requests for Flyspray and this would be yet-another-tracker to support.
##

Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/17997777-add-support-for-flyspray?utm_campaign=plugin&utm_content=tracker%2F47&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F47&utm_medium=issues&utm_source=github).

Start by reviewing how Bountysource currently supports external issue trackers, then inspect the linked Rockbox Flyspray instance to determine the required integration behavior. The issue does not identify files, tests, entry points, or acceptance criteria, so completion cannot be defined from the report alone.

Written by the indexing model from the issue text.