Link to implementation on top of the table

[jpellegrini]

Just like there is a link to the SRFI to the left of each line, the text on the top of each column, with the name of the implementation, could be clickable. No?

[lassik]

Our implementation-metadata repo knows each implementation's homepage, but that information is currently not in a uniform format. We need to unify the format; then we can scrape from that repo into this one.