build

Update library version to 1.15 and update docs #292

Job	Run time
ubuntu cmake	13s
windows (Win32, standard)	1m 20s
macos cmake	14s
ubuntu (g++, standard)	1m 7s
windows (Win32, PUGIXML_WCHAR_MODE)	1m 29s
windows (Win32, PUGIXML_COMPACT)	1m 10s
ubuntu (g++, PUGIXML_WCHAR_MODE)	1m 10s
windows (Win32, PUGIXML_NO_EXCEPTIONS)	1m 21s
ubuntu (g++, PUGIXML_COMPACT)	1m 7s
windows (x64, standard)	1m 53s
ubuntu (g++, PUGIXML_NO_EXCEPTIONS)	1m 3s
windows (x64, PUGIXML_WCHAR_MODE)	1m 7s
ubuntu (clang++, standard)	51s
windows (x64, PUGIXML_COMPACT)	1m 7s
ubuntu (clang++, PUGIXML_WCHAR_MODE)	51s
ubuntu (clang++, PUGIXML_COMPACT)	54s
windows (x64, PUGIXML_NO_EXCEPTIONS)	1m 5s
ubuntu (clang++, PUGIXML_NO_EXCEPTIONS)	48s
macos (clang++, standard)	52s
macos (clang++, PUGIXML_WCHAR_MODE)	46s
macos (clang++, PUGIXML_COMPACT)	50s
macos (clang++, PUGIXML_NO_EXCEPTIONS)	58s
	22m 16s

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