Use multi_json instead of json gem

MultiJSON allows for greater performance on CRuby (via YAJL and Oj) and
greater compatibility on other Ruby implementations. Basically, there's
no good reason not to use it. :smile:
Merge pull request #9 from sferik/multi_json

Use multi_json instead of json gem
better WebMock allow handling; version bump
use MultiJson dump for file writing
specs; Coveralls.wear! now accepts block for SimpleCov.start
spec updates
dev dependency debugger only when ruby > 1.9
empty files spec update
disable WebMock after test suite
simplecov expection typo; removed < 1.9 ruby versions in travis
circleci integration WIP
version bump
prelimenary Semaphore support
added gemfury badge
merged result support

* added wear_merged!
* added rake task
* bump version
jenkins support; filter vendor by default; version bump
peg vcr to older version
jenkins CI detection update
CI service number updates; version bump
fixes result merging w/o block [fix #12]

* preliminery codeship.io support
* version bump