WIP: Provide join_html and join_to_html. #172

Job	Run time
Rustfmt	17s
Test example (actix, stable)	44s
Test example (actix, nightly)	42s
Test example (axum, stable)	44s
Test example (axum, nightly)	46s
Test example (gotham, stable)	41s
Test example (gotham, nightly)	43s
Test example (iron, stable)	41s
Test example (iron, nightly)	38s
Test example (nickel, stable)	37s
Test example (nickel, nightly)	42s
Test example (simple, stable)	23s
Test example (simple, nightly)	19s
Test example (static-sass, stable)	18s
Test example (static-sass, nightly)	14s
Test example (statics, stable)	15s
Test example (statics, nightly)	14s
Test example (tide, stable)	1s
Test example (tide, nightly)	1s
Test example (warp03, stable)	1s
Test example (warp03, nightly)	1s
Test (stable)	24s
Test (1.64.0)	1m 8s
Test (1.60.0)	56s
Test (1.58.1)	1m 6s
Test (beta)	22s
Test (nightly)	21s
	13m 19s

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