Mutex rewrite

Fixes mutex functionality for the extension, because I'm a huge dumb and
committed something that wasn't actually working.
Hotfix

Fixes scope problem.
Working mutex solution

It's not nearly as clean as I'd like it to be, but I've finally
conceived code that should act the way the feature was intended to.
Though a previous revision "worked," it wasn't managed at an instance
level.  This one is.  Synchronized objects that have invoked the
#mutex() method will declare the instance variable @__locks__, which is
a Symbol=>Monitor Hash that contains the mutex locks for each registered
attribute.

For example, calling mutex( :sample ) will create the @sample instance
variable unless it already exists and add a wrapped writer method
(:sample=) that sets the variable inside the lock's #synchronize()
block.

Other than the new pattern for declaration within the #initialize()
method of an implementing class (or elsewhere in a module), access and
modification of variables remains otherwise the same.

(Note:  I, @florf, may be taking an extended break from development for
the time being.)
Remove defunct video playback requirements

Removes defunct video playback requirements from the Readme, adds example for using switches.
Merge pull request #12 from florf/development

Confirmed.