Add content check to HttpServiceCheck.

Introduces a new HttpServiceCheck configuration parameter called
'expect' which is string value to expect in the server response.

In addition to checking for a status code in the [200,300) range, it
also verifies a given string is contained in the response. This is similar
to the HAProxy 'http-check expect string' configuration.
Get a spec test for the example services

This checks that we can actually construct sane objects with the JSON
examples, which gives us some confidence that the examples are still
valid and we didn't forget to update them :)
Add a first initial rough cut of etcd reporter.

No real tests that this works yet, but it should be basically there..
Add documentation
Fix TTL bug
Merge pull request #50 from bobtfish/etcd_suppport

Etcd suppport
remove duplicate copy of base reporter class

we preserve the parse_data function, however.
Merge pull request #49 from wotifgroup/http-content-check

Add content check to HttpServiceCheck
Merge pull request #51 from airbnb/next_release

Next release