FEATURE: Support for decorator data that can be used in a test report by a reporter

[jenisys]

Description

Currently, the decorator works fine for already defined, built-in decorators.
But the functionality is really limited for adding new decorators to doctest.

What is missing is some kind of named annotations storage in a test case.
This mechanism would allow to store decorator name as a string to a test_case (or test_suite), like:

// — EXAMPLE:
#include <doctest/doctest.h>
#include <my_doctest_ext/decorator_verifies.h>
…
TEST_CASE(„Some test …“ * my_doctest_ext::verifies(„REQ-ID_0815“)) {
   … // — TEST IMPLEMENTATION DETAILS (left out here)
}

// — ALTERNATIVE: Direct support of annotations as test decorator
TEST_CASE(„Other test …“ * my_doctest_ext::annotation(„verifies“, „REQ-ID_0816“)) {
   … // — TEST IMPLEMENTATION DETAILS (left out here)
}

DESIRED FUNCTIONALITY:

• My own decorator stores its param(s) in the test case, like:

test_case.add_annotation(„verifies“, „REQ-ID_0815“);  // OR SIMILAR

During the test run:

• A test reporter could retrieve the annotations and show/store them in the test report
• For JUnitXML, the annotations can be stored as properties of the test-case.

OTHERWISE:

• A similar functionality with named annotations will also be needed for a test-suite (out-of-symmetry)
• NICE TO HAVE: Ability to use add_annotation(…) in the body of a test-case.