Rewrite the library to use mio and tokio (squash merge)

Squashed commit of the following:

commit 59fca19f6576af9a604b1b78a15f9a7f3902b6a0
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Mon Jun 11 11:10:11 2018 +0100

    address comments

commit 83a4bb12ed0e293f4a9b3b4effd3174d5b59b60d
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Sun Jun 10 20:17:29 2018 +0100

    change version to 0.12.0

commit 1241dd058e7be8fc52ec77b995decf9d77533b76
Merge: 8dcf79d 0b35e1da
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Thu Jun 7 13:23:44 2018 +0100

    Merge remote-tracking branch 'upstream/master'

commit 8dcf79d85d6d673c736cdf073be363f95704bf92
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Thu Jan 4 20:32:16 2018 +0000

    0.13.1: use ToSocketAddrs

commit 87f1dcc9f2be53ceeedbe7c103faca2c2b10d3e4
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Fri Dec 29 20:26:38 2017 +0000

    rip out old parsing infra, replace with nom parsers (also change headers)

commit 7f46650d42aef3db39a452f10bc72679aa3f477d
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Thu Dec 28 21:35:18 2017 +0000

    codec fixes

commit 69fa2d65e9b67ac25301205b0699b45a692ae0c2
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Thu Dec 28 20:43:57 2017 +0000

    make sends infallible

commit 11d0f4710d5341734509f13a016b3deb4e970c70
Author: eeeeeta <eeeeeta@users.noreply.github.com>
Date:   Thu Dec 28 20:34:43 2017 +0000

    let's see if this works

commit 87526368
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun Jun 5 00:17:04 2016 -0400

    Receipt handling

commit 7c321105
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Mon May 30 14:28:50 2016 -0400

    Method callback registration.

commit 053d0c7a
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun May 29 22:44:11 2016 -0400

    Adding missing files.

commit 7c3124e3
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun May 29 22:41:21 2016 -0400

    Moved dependency on mai to crates.io.

commit 4f0b7cc4
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun May 29 21:53:30 2016 -0400

    Basic support for mio 0.5.x and mai 0.1.x

commit f3127369
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun Mar 20 14:38:01 2016 -0400

    Still broken.

commit f139cd66
Author: Zack Slayton <zack.slayton@gmail.com>
Date:   Sun Feb 28 13:26:12 2016 -0500

    broken