Update docs for recent <span> and constexpr lib changes.

2019-09-09  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Update docs for recent <span> and constexpr lib changes.
	* doc/xml/manual/status_cxx2020.xml: Update p0202r3, p0858r0, p0879r0,
	p1023r0, p1085r2 status.
	* doc/html/manual/status.html: Regenerate.

From-SVN: r275522