Change notation of property names.

Property names will now follow the eBay notation in the XML.
Merge branch 'property-names' into develop
Change how service objects are constructed.

No longer need to pass a HttpClient when creating a service object.
Merge branch 'service' into develop
Correct phpdoc comments.
Merge branch 'phpdoc' into develop
Update README and add CHANGELOG.
Merge branch 'readme' into develop
Fix getting-started link in README.
Merge branch 'readme' into develop
Add link to SDK website.
Merge branch 'composer' into develop
Update code for 0.0.6 release.
Merge branch 'release-0.0.6'