Add buffer_with_time operator including tests.
Add window_with_time operator including tests.
silence warning on clang
fix clang errors in printf specs
add types_checked based on void_t proposal
add some types_checked usage
fix clang errors
stop time drift in buffer_with_time
stop time drift in window_with_time
fix clang error
ci script update
fix some warnings
add RXCPP_DELETE and types<...>
more warnings squashed
increases warning level, fixes warnings

temporarily removes combine_latest
probably breaks clang and gcc compilation
both must be fixed before pushing to master
fix clang warnings
gcc warning fixes
re-enable combine_latest

not pleased with the resulting code in observable. I want concepts :)
clang warning clean
ctest is broken on linux