add ag --width to feature-comparison

[n1vux]

re feature-comparison/index.html

per beyondgrep/ack3#234 beyondgrep/ack3#325 and old ack2 beyondgrep/ack2#596 , ability to horizontally limit context to larger than -o but smaller than whole "line" (which can be thousands with wrapped files like .js that isn't marked .min.js and any other text files with one ␤ per paragraph ) is a frequently desired feature, at least by anyone working with archived or pre-prod websites;

as such, ag --width feature seems worthy of an additional row in the comparison table