Fix version ranges in requirements.txt

remove futures which is not supported by python 3 (#381)

use bytearray instead of bytes to avoiding copying the data. (#370)

Review: maffoo@

Officially test against python 3.7 (#365)

Add support for dealing with outdated servers in the node (#343)

By "outdated" servers we mean running servers for which a newer version is available to launch. We add settings to get a information about outdated servers and to restart all outdated servers.

Review: @kunalq

Use next(it) instead of it.next() in ValueArray constructor (#329)

The .next() method no longer exists in python3.

Review: @kunalq

Update wheel configuration for py2 and py3 (#328)

Review: @kunalq

Support spawning async connections. (#302)

By pushing the spawn logic down into the async protocol instance, it
becomes possible to spawn async clients and sync clients wrapped around
async connections without using `labrad.connect`, as in ThreadedServer.

Fixes #301 
Review: @kunalq

Reject keyword args when calling packet settings.

OTS: @maffoo

Fixes: #296

Barn is a unit of area, not length (#295)