Add downloadable binaries to releases

[djfarrelly]

Purpose

For simple install, allow binaries to be curled dependent on a user's platform.

Example of how Docker Compose does this:

curl -L https://github.com/docker/compose/releases/download/1.14.0-rc2/docker-compose-`uname -s`-`uname -m` > /usr/local/bin/docker-compose
chmod +x /usr/local/bin/docker-compose

[djfarrelly]

Completed in https://github.com/bufferapp/buffer-static-upload/releases/tag/0.1.0!