Docs+Packaging: Convert our man pages to Asciidoctor.

Convert doc/*.pod to Asciidoctor. This:

* Means we use the same markup for our man pages, the guides, and
  release notes.
* Lets us add versions to our man pages.
* Gives us more formatting options, e.g. AsciiDoc supports `commands`,
  nested lists and makes it easy to include version information. The
  manpage backend doesn't seem to support tables very well,
  unfortunately.

Convert our CMake configuration to produce *roff and html man pages
using Asciidoctor. Add a "manarg" block macro which makes our synopses
wrap correctly.

Similar to the release notes, guides, and FAQ, if Asciidoctor isn't
found the man pages won't be generated or installed.

Move Asciidoctor to the list of package build dependencies in various
places.

This commit includes the conversion script (pod2adoc.py), which will be
removed later.

Line count sanity check:

Man page         .pod .adoc
androiddump       260  280
asn2deb            93  105
capinfos          401  471
captype            54   55
ciscodump         241  269
dftest             42   42
dpauxmon          153  169
dumpcap           464  534
editcap           528  583
etwdump           136  156
extcap            157  181
idl2deb            91  103
idl2wrs           120  100
mergecap          206  207
mmdbresolve        75   75
randpkt           107  111
randpktdump       158  184
rawshark          558  610
reordercap         76   78
sdjournal         145  157
sshdump           272  302
text2pcap         274  312
tshark           2135 2360
udpdump           133  151
wireshark-filter  486  479
wireshark        2967 3420

1 files changed, 38 insertions, 34 deletions

diff --git a/doc/randpkt.adoc b/doc/randpkt.adoc
index 7e65ba2445..5c7c1b3f81 100644
--- a/doc/randpkt.adoc
+++ b/doc/randpkt.adoc
@@ -1,63 +1,68 @@
-=begin man
+= randpkt(1)
+:doctype: manpage
+include::../docbook/attributes.adoc[]
+:stylesheet: ws.css
+:linkcss:
+:copycss: ../docbook/{stylesheet}
 
-=encoding utf8
-
-=end man
-
-=head1 NAME
+== NAME
 
 randpkt - Random packet generator
 
-=head1 SYNOPSIS
+== SYNOPSIS
 
-B<randpkt>
-S<[ B<-b> E<lt>maxbytesE<gt> ]>
-S<[ B<-c> E<lt>countE<gt> ]>
-S<[ B<-t> E<lt>typeE<gt> ]>
-E<lt>filenameE<gt>
+[manarg]
+*randpkt*
+[ *-b* <maxbytes> ]
+[ *-c* <count> ]
+[ *-t* <type> ]
+<filename>
 
-=head1 DESCRIPTION
+== DESCRIPTION
 
-B<randpkt> is a small utility that creates a B<pcap> trace file
+*randpkt* is a small utility that creates a *pcap* trace file
 full of random packets.
 
 By creating many randomized packets of a certain type, you can
 test packet sniffers to see how well they handle malformed packets.
 The sniffer can never trust the data that it sees in the packet because
 you can always sniff a very bad packet that conforms to no standard.
-B<randpkt> produces I<very bad> packets.
+*randpkt* produces __very bad__ packets.
 
-When creating packets of a certain type, B<randpkt> uses a sample
-packet that is stored internally to B<randpkt>. It uses this as the
+When creating packets of a certain type, *randpkt* uses a sample
+packet that is stored internally to *randpkt*. It uses this as the
 starting point for your random packets, and then adds extra random
 bytes to the end of this sample packet.
 
-For example, if you choose to create random ARP packets, B<randpkt>
+For example, if you choose to create random ARP packets, *randpkt*
 will create a packet which contains a predetermined Ethernet II header,
 with the Type field set to ARP. After the Ethernet II header, it will
 put a random number of bytes with random values.
 
-=head1 OPTIONS
-
-=over 4
-
-=item -b E<lt>maxbytesE<gt>
+== OPTIONS
 
+-b <maxbytes>::
++
+--
 Default 5000.
 
 Defines the maximum number of bytes added to the sample packet.
-If you choose a B<maxbytes> value that is less than the size of the
+If you choose a *maxbytes* value that is less than the size of the
 sample packet, then your packets would contain only the sample
-packet... not much variance there! B<randpkt> exits on that condition.
-
-=item -c E<lt>countE<gt>
+packet... not much variance there! *randpkt* exits on that condition.
+--
 
+-c <count>::
++
+--
 Default 1000.
 
 Defines the number of packets to generate.
+--
 
-=item -t E<lt>typeE<gt>
-
+-t <type>::
++
+--
 Default Ethernet II frame.
 
 Defines the type of packet to generate:
@@ -85,10 +90,9 @@ Defines the type of packet to generate:
         udp             User Datagram Protocol
         usb             Universal Serial Bus
         usb-linux       Universal Serial Bus with Linux specific header
+--
 
-=back
-
-=head1 EXAMPLES
+== EXAMPLES
 
 To see a description of the randpkt options use:
 
@@ -102,6 +106,6 @@ To generate a small capture file with just a single LLC frame use:
 
     randpkt -b 100 -c 1 -t llc single_llc.pcap
 
-=head1 SEE ALSO
+== SEE ALSO
 
-pcap(3), editcap(1)
+xref:https://www.tcpdump.org/manpages/pcap.3pcap.html[pcap](3), xref:editcap.html[editcap](1)