Added missing fields to OBX segment and improved test

The performing_organization_address and performing_organization_medical_director were both missing from the OBX segment type as you can see by looking at this OBX definition http://www.interfaceware.com/hl7-standard/hl7-segment-OBX.html

I also improved the read test to check all fields of the OBX segment
Correct badges, fixes #8
Add Ruby 2.0.0 to Travis config
Fixing indentation
Adding missing core_ext files to gemspec
Fix PID field indexes

The indexes for the PID were off by such that if you tried to call
a field like patient_dob you would get the value for previous element.

This commit fixes this issue and adds a full test for all values of a PID.
Merge branch 'fix_obx_segment'
Merge branch 'fix_patient_index'
Merge branch 'add_ruby_2_to_travis'