cmake

More docs; removed unused variables. #505

Job	Run time
linux_clang_latest	3m 5s
linux_archs (riscv64, riscv64)	16m 43s
linux_opts (gcc, no_fp)	51s
linux_archs (arm32v7, arm/v7)	16m 24s
linux_archs (arm64v8, arm64)	15m 34s
linux_opts (gcc, no_reader)	38s
linux_opts (gcc, no_writer)	47s
linux_opts (clang, no_fp)	45s
linux_archs (s390x, s390x)	15m 6s
linux_gcc5_i386	1m 27s
linux_opts (gcc, no_utf8)	1m 5s
linux_checks (Debug, Default, Valgrind)	9m 51s
linux_archs (i386, 386)	1m 47s
linux_checks (Release, Default, Valgrind)	2m 58s
linux_opts (clang, no_writer)	34s
linux_checks (Release, ReduceBinary, Valgrind)	6m 40s
linux_gcc4	1m 19s
linux_checks (Debug, ReduceBinary, Valgrind)	8m 32s
linux_checks (Debug, Default, Sanitizer)	2m 49s
linux_opts (clang, no_reader)	32s
linux_checks (Debug, ReduceBinary, Sanitizer)	1m 21s
linux_checks (MinSizeRel, Default, Valgrind)	3m 26s
windows_msvc	2m 25s
linux_checks (MinSizeRel, ReduceBinary, Valgrind)	7m 1s
linux_opts (clang, no_utf8)	51s
linux_archs (ppc64le, ppc64le)	13m 8s
macos_clang	33s
linux_gcc_latest	3m 9s
linux_checks (MinSizeRel, ReduceBinary, Sanitizer)	1m 31s
linux_checks (Release, Default, Sanitizer)	2m 0s
linux_checks (Release, ReduceBinary, Sanitizer)	1m 44s
fuzzing	5m 24s
linux_checks (MinSizeRel, Default, Sanitizer)	1m 58s
linux_tinycc	43s
codecov	58s
	2h 33m 39s

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