syriaca-headword and Wilmshurst XSLT

I added the global attribute @xml:lang="en" in the header, I replaced
"syriaca-authorized" with "syriaca-headword" to indicate our preferred
forms, and I updated place-spreadsheet2tei.xsl to deal with Wilmshurst
data.  I still need to refine the .xsl to deal with Wilmshurst columns
referring to URIs rather than to place names.