Simpler connect

[wallyqs]

Adds support for connecting to NATS, following similar usage as in the latest Go client and still backwards compatible with options based connect API.

    # Only specifying endpoint uses NATS default scheme and port.
    NATS.connect("demo.nats.io") do |nc|
      # ...
    end

    # Setting custom server URI to connect.
    NATS.connect("nats://localhost:4222") do |nc|
    end

    # Setting username and password to authenticate.
    NATS.connect("nats://user:password@localhost:4222") do |nc|
      # ...
    end

    # Specifying explicit list of servers via options.
    NATS.connect(servers: ["nats://127.0.0.1:4222","nats://127.0.0.1:4223","nats://127.0.0.1:4224"]) do |nc|
      # ...
    end

    # Using comma separated array to define list of servers.
    NATS.connect("nats://localhost:4223,nats://localhost:4224") do |nc|
       # ...
    end

    # Setting infinite reconnect retries with 2 seconds back off against custom URI.
    NATS.connect("demo.nats.io:4222", max_reconnect_attempts: -1, reconnect_time_wait: 2) do |nc|
      # ...
    end