Fix citation link for ACM Transactions on Mathematical Software

[tyronerees]

The link didn't work - now fixed!

[tyronerees]

The error is in the generated html files too. When I regenerate locally, I've got lots of warnings and errors, especially for the C version, and the diff between the versions is huge. @jfowkes @AdamG412 @AndrewLister-STFC: do you either (a) have a local configuration that works for this, or (b) want me to just manually edit the html files to add the missing character to fix the broken links?

[jfowkes]

@tyronerees I do have a local configuration that works for this but not without errors, probably quickest just to make the one-character edit to the html? Also happy to recompile if you prefer. The main issue with the docs is that:

• the Fortran docs use a long-abandoned attempt to get Sphinx working for Fortran (the docs look okay but the extension doesn't play nicely with modern Sphinx and this is only going to get worse)
• the C docs have some issues with duplicate names in the SSMFE documentation which screws up some links (see the very first issue: Duplicate entity definitions in sphinx docs #1)

As I think we discussed for HSL there are no good solutions for getting Fortran to work with Sphinx afaik.