Bring Junit tests to Java 1.6 compatibility

[stleary]

What problem does this code solve?
The project code is 1.6-compatible, but the unit tests require Java 1.7. This makes building and testing clumsy, and
can't be sure the lib works correctly in a Jave 1.6 environment. Remove diamond operators: <> and
autoclose expressions from several junit modules. Updated Maven pom.xml to use Java 1.6.
Confirmed that Maven (1.6) and Gradlew (1.8) build and test correctly.

Risks
No risk to production code, moderate risk to unit tests.

Changes to the API?
No

Will this require a new release?
No

Should the documentation be updated?
Yes - readme will need to be updated, but it's currently in review on another branch.
CI build will be updated on approval/merge, to add testing to the 1.6 build.

Does it break the unit tests?
No

Was any code refactored in this commit?
No

Review status
Approved - by myself

[stleary]

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