Connection cache for producer

[iproctor]

Optionally globally cache connections to a host:port.

Connecting/reconnecting was broken into a separate Connection object. This is what is cached. Many Producers can share one Connection. The original event generation behavior was preserved.

The producer test runs twice, with and without caching. New tests were added with a mock socket to test edge cases.

[Raynos]

The travis build failed because node 0.9 doesn't exist on travis. It works fine in 0.8 and 0.10

[cainus]

This is some awesome work. I've got a bunch of minor concerns:

• Did you run up against this issue on 0.11?
• I'm generally not a huge fan of soft-coded dependency versions relying on semver adherence. I've just been burned too many times by bad adherence breaking stuff. Any issue with hard-coding your readable-stream version?
• In your production use, have you seen this?
• It'd be ideal to get that travis build passing before merge too. Feel free to change the .travis.yml to have 0.11 instead of 0.9.

Again, just minor stuff. I really appreciate all this awesome work.

[cainus]

It turns out that that buffermaker issue is a legit issue on 0.11 that bignum doesn't have a fix for yet. So I'm considering swapping out bignum for long or bignumber. Do you have a preference? Do you want to check performance of these first?

[Raynos]

set this to 1.0.26 or something.

[Raynos]

@cainus we dont run 0.11 in production.

I think supporting 0.11 is out of scope for this PR.

We will look into 0.11 support once 0.12.0 is released.

The package.json thing is a good idea, we'll fix that.

[cainus]

Alright... I've merged this in. I have a bit of upkeep to take care of before I publish, but that'll be in the next day or so.

And hey... a README update would be fantastic as well, if you're up for it.

[Raynos]

@cainus updated the README.

If you can publish a new version soon that would be great :)

[cainus]

Alright... published as 0.7.0! Thanks guys! I added you as contributors on the repo as well.