Request for CppUTest support

[claremacrae]

We've had a request for support of CppUTest from James Grenning - @jwgrenning -

I'd like to see CppUTest able to use Approvals.

From the current Meeting C++ survey results, it gets a mention (10 out of 684 responses)...

https://meetingcpp.com/mcpp/survey/results.php?q=61

[claremacrae]

Progress report:

• [x] CppUTest support is implemented...
• [x] I could easily add support for the user to supply their own main, which I think may be a reasonably common thing to do
• [x] I need to add the docs for this feature
• [x] ABANDONED Remove the need to turn off CppUTest's memory-leak checking due to likely false-positives
  • One of the CppUTest authors has confirmed that the ApprovalTests code isn't leaking memory, and the issue is to do with the interaction of the implementation of the CppUTest leak-checks and how some STL implementations manage memory lifetime. Unfortunately I'm going to have to put this down, due to time limitations,
• [x] Fix #160 - Boost tests are failing to run on Mac
• [ ] Fix #161 - on AppVeyor, the code doesn't build on Cygwin
  • For now, I've disabled the CppUTest build on CygWin

[claremacrae]

The implementation of this is now merged to the main branch.

Docs are available at:

• https://github.com/approvals/ApprovalTests.cpp/blob/master/doc/UsingCppUTest.md#top
• https://approvaltestscpp.readthedocs.io/en/latest/generated_docs/UsingCppUTest.html

I'm closing this now - it will be included in the next release.