Update description of x.5.1 and 1.5.2 changes.
improve HTML anchors conditioning

Put all sed commands into a temporary script file and call sed only once
per HTML file. Replace most hardcoded sed commands with a few code
blocks. Add a code block to convert 3PCAP manpages references into
hyperlinks.
regenerate manpages

This update incorporates recent updates to libpcap manpages and
regen_manpages.sh