Enable / Disable EMG streaming

[aarontabor]

Currently, EMG streaming begins when an instance of MyoEMG is created, and continues for entirely of the object's existence. In practice this will probably be unnecessarily demanding on the armband's battery life, and a mechanism to enable/disable streaming should be added to the MyoEMG class.

Proposed Solution

Add instance methods enableEmgStreaming() and disableEmgStreaming() to the MyoEMG class. EMG streaming can be enabled/disabled by subscribing/unsubscribing to notifications from the 4 EMG Data channels.

[aarontabor]

See the class constructor for an example of subscribing to notifications.

• To subscribe, write the message 0x01 0x00 to the appropriate handle
• To unsubscribe, write the message 0x00 0x00 to the appropriate handle