docs: minor doxygen updates and fixes #146

Job	Run time
Make (gcc)	1m 29s
Make (gcc, USE_STANDARD_TMPFILE=1)	1m 24s
Make (gcc, USE_SYSTEM_MINIZIP=1)	1m 56s
Make (gcc, USE_DTOA_LIBRARY=1)	1m 30s
Make (gcc, USE_NO_MD5=1)	1m 45s
Make (gcc, USE_OPENSSL_MD5=1)	1m 33s
Make (gcc, USE_MEM_FILE=1)	2m 0s
Make (clang)	2m 12s
Make (clang, USE_STANDARD_TMPFILE=1)	1m 39s
Make (clang, USE_SYSTEM_MINIZIP=1)	1m 47s
Make (clang, USE_DTOA_LIBRARY=1)	1m 52s
Make (clang, USE_NO_MD5=1)	1m 38s
Make (clang, USE_OPENSSL_MD5=1)	1m 56s
Make (clang, USE_MEM_FILE=1)	1m 42s
	24m 23s

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