Add documentation for:

* Requirement Rules; std::locale-support, std::facet-support, and common-variant-tag
* Install Descriptions; install, install-subinclude, and install-source.


[SVN r20824]

tools/build

@@ -1 +1 @@
-Subproject commit c73a3a7324f48da6e721f30936fea69f6805f100
+Subproject commit bd35768f727bd720b48b137105bca64c9ddf0894