PV1 segment cleanup and specs.
spec for PV1, add in convert_to_ts usage for date fields.
PID segment cleanup and specs.
spec for PID (in particular the patient name) , remove idx from segment definition(supplied idx was buggy), added missing fields.
MSH segment cleanup and specs.
spec for msh, remove idx from segment definition, added missing fields, remove convert_to_ts (use superclass)
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.