PULL_REQUEST_TEMPLATE.md

What does this implement/fix? Explain your changes.

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Does this close any currently open issues?

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Any other comments?

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Checklist

Check all those that are applicable and complete. Put an x between the brackets (without spaces).

• Merged with latest master branch
• Add change details to CHANGELOG.md
• Added new test to spec directory
• Travis & Appveyor CI passes (Linux/Windows support)