Added Mute Option and Solved #21

[quozl]

Thanks, but I'm not quite sure what many of your the changes are for. See Files changed for what I'm looking at.

[quozl]

Thanks, but the explanation of your changes should be in the commit message. Your existing commit message did not mention many of the things that you had since said. See Making commits for guidance.

After you explained the changes I was able to see your purpose more clearly, and realised that you had fixed more than one problem in your one commit. This makes it harder to review. Try to use different commits for different fixes, as it makes it easier to write commit messages for them.

As of c4769d7 the work remaining is;

• [ ] return instead of calling exit,
• [ ] new code should comply with flake8,
• [ ] rewrite the commits and use communicative commit messages,

Suggested commit messages;

Add mute key feature

Add m key to instructions.  Respond to the m key by toggling sound.

Repair exit path

Problem: (actually don't yet know why you changed this, so looking forward to your words)

Solution: 

Fix keys are missing

Some key events were missed, and the game would not respond.

Events were dequeued twice in the event loop.

Fixes: URL

[aditya113141]

I will close this and open new one. I messed up somewhere.

[quozl]

https://github.com/sugarlabs/flappy-birds-activity/pull/24