Although get_value() calls with a reference, pointer, or C-style array type are not supported, but actual attempts of such calls emit user-unfriendly compile error messages.
So, in this PR, static_asserts have been added to detect those types and emit an error message which clearly states they are unsupported.
The documentation pages for get_value() and get_value_ref() APIs have also been updated to clarify type restrictions.

Pull Request Checklist

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• Changes are described in the pull request or in a referenced issue.
• The test suite compiles and runs without any error.
• The code coverage on your branch is 100%.
• The documentation is updated if you added/changed a feature.

Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
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