Create wrapper ApprovalTests.hpp for projects that use this via add_subdirectory (or similar) to use

[claremacrae]

For the background to this, see
approvals/ApprovalTests.cpp.StarterProject#9

It turns out that this will be really useful when documenting the CMake Integrations - see #69.

[claremacrae]

Unfortunately adding a single header for ApprovalTests has broken the Xcode CI builds that use unity.

https://github.com/approvals/ApprovalTests.cpp/runs/393170720
https://github.com/approvals/ApprovalTests.cpp/runs/393170749

Commenting out this one test fixes the build:

// begin-snippet: YouCanVerifyCombinationsOf2
TEST_CASE("YouCanVerifyCombinationsOf2")
{
    std::vector<std::string> v{"hello", "world"};
    std::vector<int> numbers{1, 2, 3};
    CombinationApprovals::verifyAllCombinations(
        [](std::string s, int i) { return std::make_pair(s, i); }, v, numbers);
}
// end-snippet

This is probably related to catchorg/Catch2#1405 "Fixes disagreement between operator<< available for SFINAE and actually usable"

[claremacrae]

The fix in a877b87 didn't entirely work. The code built, but tests in CombinationTests.cpp failed to find the source code location when in Ninja Unity builds - the file was compiled on its own, so must not have had whatever magic Ninja and Unity uses to get the path right when multiple files are compiled.

The next change - 8a94fa8 - built fine and the tests passed.

[claremacrae]

I've logged the need for a workaround to the build failure in #90 - so am closing this issue now.