Refactor Kinetic lib

[adrienverge]

Refactor Kinetic lib for static constants and PDU class

Big refactor of the Kinetic library:

• move constants out of instances (memory footprint)
• give a proper name to instances (Kinetic.PDU)
• modify tests consequently
• document library usage in README.md:

Fixes: #18

---

Kinetic: Define PDU commands as classes

Currently to create a "PUT" Kinetic PDU, one must run:

const pdu = new Kinetic.PDU();
pdu.put();

This is not object-oriented programming, and is error-prone since we don't expect commands like put, flush etc. to create messages with a given type.

This patch creates classes that inherit from PDU, e.g. PutPDU, GetPDU, GetLogPDU etc. and that can be used the same way.

---

Sample from README:

import Kinetic from 'Kinetic';

const rawData = new Buffer('\x46\x00\x00\x00\x32\x00');
const kineticPDU = new Kinetic.PDU(rawData);

if (kineticPDU.getMessageType() === Kinetic.ops.GET) {
    const response = new Kinetic.PutPDU('key', 1, null, '1', 0);
    response.setChunk(new Buffer('value'));

    const sock = net.connect(1234, 'localhost');
    const ret = response.send(sock);
    if (ret !== Kinetic.errors.SUCCESS)
        throw new Error("argh: " + Kinetic.getErrorName(ret) + "!");
}

[ghost]

LGTM. Good work on refining that library.

[adrienverge]

Thanks @MichaelZapataScality. I'm currently adding some more changes to this PR so @AntoninCoulibaly and I can write unit tests on sane basis.

[koolfunky]

👍 Nice refactor ;)

[adrienverge]

Ready for review from you @MichaelZapataScality 🔎 ;-)

[ghost]

response.send(sock) ? I might be too used to the sock.send(response) architecture, but it looks strange to me, in OOP terms.

[adrienverge]

I did not change this. This PR is a refactor only.

[ghost]

okay, might be for another round then :)

[ghost]

Despite all my remarks that are not completely relevant to this PR (due to the fact that I've never reviewed any code from Kinetic PRs until now), I'm ok with this PR, though I think it will require a cleanup soon enough, for which I'm ready to make myself available to discuss the different details I commented here.
So in the meantime, for this PR 👍

[adrienverge]

@DavidPineauScality Thanks for your comments, I addressed them.

Everything should be fine now.

[ghost]

👍