Add support for modular build structure. #147

Job	Run time
posix (gcc-11, 2a, ubuntu-22.04)	3m 46s
posix (gcc-12, 20,2b, ubuntu-22.04, g++-12)	7m 54s
posix-cmake-subdir (ubuntu-22.04, OFF, 0)	42s
posix (gcc-13, 20,2b, ubuntu-latest, ubuntu:23.04, g++-13)	8m 4s
posix-cmake-subdir (ubuntu-22.04, ON, 0)	35s
posix (clang, clang++-14, 20,2b, libc++, ubuntu-22.04, clang-14 libc++-14-dev)	1m 5s
posix-cmake-test (ubuntu-22.04, OFF, 0)	3m 27s
posix-cmake-subdir (macos-13, OFF, 1)	1m 24s
posix (clang, 20,2b, macos-13, libc++, boost-container)	1m 59s
posix-cmake-test (ubuntu-22.04, ON, 0)	3m 31s
posix-cmake-install (ubuntu-22.04, OFF, 0)	45s
posix-cmake-install (ubuntu-22.04, ON, 0)	43s
posix-cmake-test (macos-13, OFF, 1)	4m 10s
posix-cmake-subdir (macos-13, ON, 1)	2m 4s
posix-cmake-install (macos-13, OFF, 1)	1m 29s
posix-cmake-test (macos-13, ON, 1)	3m 58s
windows (msvc-14.3, 20,latest, 32,64, windows-2022)	17m 52s
posix-cmake-install (macos-13, ON, 1)	1m 57s
windows (gcc, 2a, 64, windows-2019)	2m 18s
windows-cmake-install (windows-2022, OFF)	2m 20s
windows-cmake-subdir (windows-2022, OFF)	2m 33s
windows-cmake-install (windows-2022, ON)	3m 13s
windows-cmake-test (windows-2022, OFF)	7m 51s
windows-cmake-test (windows-2022, ON)	8m 39s
	1h 32m 19s

Provide feedback