Remove last bits of Xhtml.
Remove the plus type.
And even more other plus.
Slightly more plus cleanup.
Merge branch 'remove_xhtml' into new_wrap
Merge branch 'clean_svg' into new_wrap

Conflicts:
	lib/svg_f.ml
	lib/svg_sigs.mli
Merge branch 'clean_html5' into new_wrap

Conflicts:
	lib/html5_f.ml