add RFC97: dynamically create high zoom level tiles

c.f. mapserver/mapcache#63
add Boston sprint changes from #28
more Boston sprint changes related to #28
remove mapcache and tinyows references in documentation page as per discussions in #28
re-add mapcache and tinyows links according to latest discussions in #28
Added text and expression functions for PHP and fixed name error for expression function in swig (#39)
Added link to 6.2.1 release.
Updating for 6.2.1 release.
Added link to 6.2.1 changelog.
update for 6.2.1 release
update for 6.2.1 release
update RFC95 status

mapserver/mapserver#4648
Merge branch 'branch-6-2'

Conflicts:
	en/documentation.txt
	en/index.txt
add list expression documentation (rfc95)

mapserver/mapserver#4648