Refactor tests related to subject and sub

[MitMaro]

For #492

This change extracts all tests in the existing files related to the subject option and sub claim into a single test file. Several other tests are also added that were missing from the existing files.

I removed all references to "subject" and "sub" from the existing test files that I could find.

There seems to be only minimal validation on the subject claim. The next major version could handle adding validation to this claim.

As always, suggestions or missing tests are welcome!

Coverage Master

=============================== Coverage summary ===============================
Statements   : 97.87% ( 230/235 )
Branches     : 97.55% ( 199/204 )
Functions    : 100% ( 23/23 )
Lines        : 98.28% ( 228/232 )
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Coverage Branch

=============================== Coverage summary ===============================
Statements   : 97.87% ( 230/235 )
Branches     : 97.55% ( 199/204 )
Functions    : 100% ( 23/23 )
Lines        : 98.28% ( 228/232 )
================================================================================