Aserver-nodes

[thomas-hermann]

The current Aserver doesn't allow to free a scheduled or playing signal.
For the branch Aserver-nodes, I propose

• to add automatic node_id allocation for any played asig
  • this will require the introduction of a src_nodes list
• Aserver.play() to return that node_id (Asig.play() to store it in its context dict (_['node_id'])
• service functions to interact with existing nodes, e.g.
  • free_all(): to remove all scheduled and playing entries
  • free(node_id): to remove a specific node_id
  • ... (any other useful suggestion?)
    I have added a threading.Lock(), hope I have secured all critical parts...

A code could be

alongsig1.play()
node = alongsig1._['node_id']  # later with Metadata:  node = alongsig1.info.node_id
alongsig2.play()
s.free(node)  # at a later time
# alongsig2 will keep playing...

• So far only free_all() works. Please try it and comment.