Implements tests for H5Dread_multi / H5Dwrite_multi (#57) #52

Job	Run time
Ubuntu GCC REL	2m 15s
Ubuntu GCC DBG	1m 43s
Ubuntu GCC parallel (build only) REL	2m 42s
Ubuntu GCC parallel (build only) DBG	2m 10s
MacOS Clang REL	3m 54s
Ubuntu GCC -Werror Debug (build only) DBG	1m 42s
Ubuntu GCC -Werror Release (build only) REL	2m 9s
Ubuntu GCC -Werror Debug parallel (build only) DBG	2m 15s
Ubuntu GCC -Werror Release parallel (build only) REL	2m 48s
	21m 38s

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