worksheet: add initial embedded image support #170

Job	Run time
Make (gcc)	1m 22s
Make (gcc, USE_STANDARD_TMPFILE=1)	1m 23s
Make (gcc, USE_SYSTEM_MINIZIP=1)	1m 23s
Make (gcc, USE_DTOA_LIBRARY=1)	1m 27s
Make (gcc, USE_NO_MD5=1)	1m 19s
Make (gcc, USE_OPENSSL_MD5=1)	1m 35s
Make (gcc, USE_MEM_FILE=1)	1m 29s
Make (clang)	1m 36s
Make (clang, USE_STANDARD_TMPFILE=1)	1m 36s
Make (clang, USE_SYSTEM_MINIZIP=1)	1m 38s
Make (clang, USE_DTOA_LIBRARY=1)	1m 41s
Make (clang, USE_NO_MD5=1)	2m 14s
Make (clang, USE_OPENSSL_MD5=1)	1m 46s
Make (clang, USE_MEM_FILE=1)	1m 35s
	22m 4s

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