Add support for image and link URL rewriting #1086

Job	Run time
build_lib_test (nightly)	51s
build_lib_test (beta)	1m 8s
build_lib_test (stable)	1m 8s
build_lib_test ($MSRV)	3m 4s
build_bin_spec (nightly)	1m 10s
build_wasm (nightly)	46s
build_wasm (beta)	47s
build_wasm (stable)	42s
build_bin_spec (beta)	1m 12s
build_wasm ($MSRV)	2m 30s
build_bin_spec (stable)	1m 2s
build_bin_spec ($MSRV)	2m 44s
clippy_format	2m 6s
lockfile	58s
no_features_build_test (nightly)	32s
no_features_build_test (beta)	31s
no_features_build_test (stable)	24s
no_features_build_test ($MSRV)	1m 59s
	23m 34s

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