Updated documentationsandbox/ctxnop/docs

Added documentation up to date and using the gitbook format.

Change-Id: Ie5d6a3bb489b9a9a95e21f5edd05bdd77bff5816
Signed-off-by: Loïc Collignon <loic.collignon@iot.bzh>

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+# Concepts
+A user application requests to open an audio role, which is bound to a stream, which is bound to a zone. This allows the application to only care about the audio role.
+
+For example, a navigation application can request the **navigation** role, which is bound to the **navigation** stream defined by the HAL. This stream is bound to the **driver** zone, which is the closest speaker to the driver.
+
+## Roles
+The high level API allows applications to open roles such as **emergency**, **navigation** or **multimedia**. A role is bound to a stream, which is basically a device URI. When a role is opened, then the policy engine is notified and executes an interrupt on every other opened roles with a lower priority. An interrupt is a policy engine function that can change the volume, mute or unmute, change the stream's state.
+
+This behaviour allows the policy engine to take actions like lowering the radio volume when an application wants to play something on the emergency role.
+
+## Streams
+A stream is basically a device URI that you can open to write audio data. For exemple, it can be "hw:2,0,1", which means that you have to use this as an alsa device URI.
+
+## Zones
+Multiple speakers are spread arround inside a vehicule, they are named depending on their position, like **front-center**, **front-left**, **front-right**, **rear-left**, **rear-right**, etc... 
+Zones are an abstraction of positional audio. A zone is made of one or more speakers and describes logical audio areas like **driver**, **front**, **rear**, etc.