CMake

Factor-out XML escaping routines into a separate file (xml_escape.c) … #212

Job	Run time
Windows, shared, x64, with tests	11m 31s
Windows, shared, x64, vs2022, with tests	12m 15s
Windows, shared, x86	3m 32s
Windows, static, x64, with tests	10m 58s
Linux, shared, with tests	3m 45s
	42m 1s

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