HTTP response format continued

[mreiferson]

@jehiah noticed that we didn't update nsqlookupd HTTP response formats in #330

took advantage of the opportunity to make the code a little more modular and reusable

[jehiah]

LGTM. ready for this to land?

[mreiferson]

not yet, gonna do the forwards/backwards compatibility crap between daemons

[mreiferson]

btw, I have to do this anonymous function junk to maintain compatibility with go1.0.3

[jehiah]

much appreciated =).

inching closer to not needing that.

[mreiferson]

I have a bit more work to do here but this is the last PR I'd like to get in for this next release

[mreiferson]

this is ready for review, but I intend on doing a few more things:

• manually give this a test run
• get some tests written for old/new HTTP endpoints for nsqd and nsqlookupd

[jehiah]

Technically we could put this in the actual content-type response "application/json; charset=utf-8; nsq-version=1.0"

[mreiferson]

I would be worried about shitty HTTP clients that this might screw up...

I copied the GitHub API, FWIW.

[jehiah]

Changes look pretty sane to me.

[mreiferson]

OK, RFM @jehiah

I've deferred the nsqadmin tests to #323 - but I've tested it manually with and without nsqlookupd and with old and new versions.