* fixed flags in RUN declaration in lit test
* added tests for C++20 concepts and requires clause
* added manual tokenization for AutoType return types which are not plain 'auto' to find source range
- 'const auto'
- 'Concept<int> auto'
- 'decltype(auto)'
* improved formatting of documentation
* support for 'decltype(...)'
* added test for bug 44206, which seems to be fixed