Add support for modular build structure. (#192) #153

Job	Run time
posix-cmake-install (ubuntu-22.04, OFF, 0)	48s
posix (gcc-11, 2a, ubuntu-22.04)	3m 45s
posix-cmake-install (ubuntu-22.04, ON, 0)	41s
posix-cmake-subdir (ubuntu-22.04, OFF, 0)	1m 20s
posix (gcc-12, 20,2b, ubuntu-22.04, g++-12)	7m 49s
posix-cmake-test (ubuntu-22.04, OFF, 0)	3m 44s
posix-cmake-install (macos-13, OFF, 1)	1m 56s
posix-cmake-subdir (ubuntu-22.04, ON, 0)	35s
posix (gcc-13, 20,2b, ubuntu-latest, ubuntu:23.04, g++-13)	7m 35s
posix-cmake-install (macos-13, ON, 1)	2m 1s
posix-cmake-test (ubuntu-22.04, ON, 0)	3m 51s
posix-cmake-subdir (macos-13, OFF, 1)	1m 54s
posix (clang, clang++-14, 20,2b, libc++, ubuntu-22.04, clang-14 libc++-14-dev)	7m 15s
posix-cmake-test (macos-13, OFF, 1)	4m 35s
posix-cmake-subdir (macos-13, ON, 1)	1m 30s
posix (clang, 20,2b, macos-13, libc++, boost-container)	7m 33s
posix-cmake-test (macos-13, ON, 1)	4m 48s
windows (msvc-14.3, 20,latest, 32,64, windows-2022)	17m 54s
windows-cmake-install (windows-2022, OFF)	2m 32s
windows (gcc, 2a, 64, windows-2019)	1m 50s
windows-cmake-subdir (windows-2022, OFF)	2m 22s
windows-cmake-install (windows-2022, ON)	2m 45s
windows-cmake-test (windows-2022, OFF)	8m 5s
windows-cmake-test (windows-2022, ON)	8m 32s
	1h 45m 40s

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