style.9: Reference style.lua(9) and both Emacs and Vim indentation plugins

[0mp]

Summary

Changes:

• Add a FILES sections. Reference Emacs and Vim indentation plugins there, which are present in the src tree.
  • I used an absolute path as it seems to be the way to reference files from the source tree I've seen in other manpages.
  • I did not use -width "..." -compact on the .Bl macro because the resulting formatting is hardly readable.
• Add style.lua to the SEE ALSO section.

[0mp]

After running mandoc -Tlint on the previous patch it turned out that there are two issues to be addressed:

• .Tn macro usage is discouraged so do not use .Tn.
• .Bl -tag requires -width. Set it to -width indent.