threadsafe.html section headers do not have preserved case

[jay]

The thread safety webpage, which curl-www generates by running roffit on libcurl's docs/libcurl/libcurl-thread.3, has had section header 'TLS' casing changed by roffit to 'Tls':

Starting in roffit 0.13 (bagder/roffit@5b5b044) --preserve-case is needed to preserve the case of section headers. IMO this is a header that needs casing preserved so it shows as 'TLS'.

https://github.com/curl/curl-www/blob/06151e835d1531fc7485e72d1081abd451b267f1/libcurl/c/Makefile#L481-L482

Unfortunately it doesn't look as simple as appending --preserve-case to $(MAN2HTML)

https://github.com/curl/curl-www/blob/06151e835d1531fc7485e72d1081abd451b267f1/libcurl/c/Makefile#L18-L20