New task tracker

[Laurent]

The new task tracker is online:
https://github.com/SFML/SFML/issues

I chose not to add the old tasks, I'm restarting from zero now.

So, how does it work:
- login to github
- go to the SFML task tracker page
- click "Create issue"
- fill the title and description; labels must be added by an admin (me)
- I'll inspect every new tasks, and comment/reject it if necessary
- you can also vote for tasks that you like

So... feel free to add tasks for bug reports or features requests.

[Nexus]

I chose not to add the old tasks, I'm restarting from zero now.

Nice, everything solved

I've added the angle issue, by the way.

[Hiura]

I've just added some issues to represent the state the OS X development. Don't hesitate to add some more if you find anything suspect with this implementation.  :wink: