Revise DDL entries with upsrw/upscmd comments to use RW and CMD keywords

[jimklimov]

Primarily mea culpa about earlier commits as I was learning this corner of the NUT ecosystem and amassing DDL info from github issues and mailing list posts.

Also check about "Source:" and "Vendor:" headers used in many older files to streamline links to NUT issues and Vendor product pages, maybe document those as a markup standard?

[jimklimov]

After the merge of #33 (as well as networkupstools/nut#2006 to generate and networkupstools/nut-website#42 to handle the new markup), the nut-ddl contents should make it relatively easy to find and fix the "unstructured" variable and command reports.

Note that currently the NUT tools/nut-ddl-dump.sh provides such information as direct dumps from upsrw and upscmd (there are now 3 reports which state that they come from the script, and may more tagged with DEVICE:COMMENT-BLOCK:FIXME:(UPSRW|UPSCMD): overall). If there are later efforts to automate production of #CMD:..., #RW:... and #RO:... comments to convert existing and incoming reports, it may be worthwhile to address them in that script too.