Support asynchronous send API

[rshivane]

It would be very convenient to have an asynchronous send client, that could buffer data points and send them as a batch, like in the sample below.

The async client could have a param (max_datapoints_in_mem) that controls the max number of data points to keep in memory. A send is triggered if the memory limit is reached.

The client could have another param (max_wait_time) that controls the max amount of time to buffer the points locally before sending. A send is triggered if the wait time is reached.

client = AsyncSender(Apptuit(token=token), max_datapoints_in_mem=10000, max_wait_time=5)

metrics = ["proc.cpu.percent", "node.memory.bytes", "network.send.bytes", "network.receive.bytes", "node.load.avg"]
tags = {"host": "localhost", "ip": "127.0.0.1"}
curtime = int(time.time())
while True:
    curtime = int(time.time())
    for metric in metrics:
        client.send(DataPoint(metric, tags, curtime, random.random()))
    time.sleep(60)