doc/sphinx/formats: Add "schema" extlink
merge dev_4_4 -D org -I include -E exclude: PR 379 (Fix source code links moved to the scifio-tools foder)
merge dev_4_4 -D org -I include -E exclude: PR 444 (ScanR: fix well linkage issues)
merge dev_4_4 -D org -I include -E exclude: PR 445 (TIFF: correct for invalid tile heights)
merge dev_4_4 -D org -I include -E exclude: PR 448 (Add "schema" extlink (dev_4_4))