update HTML man pages

Update text in existing files for:
* pcap_breakloop.3pcap
* pcap_loop.3pcap
* pcap_offline_filter.3pcap

Add new files for:
* pcap-config.1
* pcap_set_immediate_mode.3pcap

In the rest of .html files remove needless Content-type header.
update TXT man pages

Regenerate all .txt files using the current contents of man pages. This
also converts the encoding to ASCII.