documentation: adaptions for asciidoctor (ifdefs, literal blocks)

When using asciidoctor, backend "manpage" (-b manpage) is used, while
a2x converts asciidoc to docbook (xml), then manpage.

Asciidoctor creates ugly indentation for [literal] blocks in SYNOPSIS,
use [verse] instead.

doc/btrbk.1.asciidoc

@@ -15,7 +15,7 @@ btrbk - backup tool for btrfs subvolumes
 SYNOPSIS
 --------
 
-[literal]
+[verse]
 btrbk [-h|--help] [--version]
       [-c|--config <file>] [-n|--dry-run]
       [-p|--preserve] [--preserve-snapshots] [--preserve-backups]
@@ -240,7 +240,7 @@ The following table gives a quick overview of the action commands and
 resulting snapshot creation (S+), backup creation (B+), snapshot
 deletion (S-), and backup deletion (B-):
 
-ifdef::backend-docbook[]
+ifdef::backend-docbook,backend-manpage[]
 ....
 Command   Option                 S+ B+ S- B-
 --------------------------------------------
@@ -258,8 +258,8 @@ prune                                  x  x
 prune     --preserve-snapshots            x
 prune     --preserve-backups           x
 ....
-endif::backend-docbook[]
-ifndef::backend-docbook[]
+endif::backend-docbook,backend-manpage[]
+ifndef::backend-docbook,backend-manpage[]
 [cols="2*<m,4*^", options="header,autowidth,compact", style="monospaced"]
 |=======
 |Command  |Option                |S+ |B+ |S- |B-
@@ -277,7 +277,7 @@ ifndef::backend-docbook[]
 |prune    |--preserve-snapshots  |   |   |   | x
 |prune    |--preserve-backups    |   |   | x |
 |=======
-endif::backend-docbook[]
+endif::backend-docbook,backend-manpage[]
 
 
 === Informative Commands
@@ -298,9 +298,9 @@ file system.
 Available subcommands:
 +
 --
-ifndef::backend-docbook[]
+ifndef::backend-docbook,backend-manpage[]
 [horizontal]
-endif::backend-docbook[]
+endif::backend-docbook,backend-manpage[]
 
 *snapshots*;; List all snapshots (and corresponding backups). Note
               that all snapshots related to configured subvolumes are
@@ -381,9 +381,9 @@ EXIT STATUS
 
 *btrbk* returns the following error codes:
 
-ifndef::backend-docbook[]
+ifndef::backend-docbook,backend-manpage[]
 [horizontal]
-endif::backend-docbook[]
+endif::backend-docbook,backend-manpage[]
 0::   No problems occurred.
 1::   Generic error code.
 2::   Parse error: when parsing command-line options or configuration

doc/btrbk.conf.5.asciidoc

@@ -15,7 +15,7 @@ btrbk.conf - btrbk configuration file
 SYNOPSIS
 --------
 
-[literal]
+[verse]
 /etc/btrbk.conf
 /etc/btrbk/btrbk.conf
 
@@ -106,9 +106,9 @@ otherwise.
     names. Defaults to ``short''.
 +
 --
-ifndef::backend-docbook[]
+ifndef::backend-docbook,backend-manpage[]
 [horizontal]
-endif::backend-docbook[]
+endif::backend-docbook,backend-manpage[]
 *short*;;    +YYYYMMDD[_N]+  (e.g. "20150825", "20150825_1")
 *long*;;     +YYYYMMDD<T>hhmm[_N]+  (e.g. "20150825T1531")
 *long-iso*;; +YYYYMMDD<T>hhmmss&plusmn;hhmm[_N]+  (e.g. "20150825T153123+0200")

doc/ssh_filter_btrbk.1.asciidoc

@@ -15,7 +15,7 @@ ssh_filter_btrbk - ssh command filter script for btrbk
 SYNOPSIS
 --------
 
-[literal]
+[verse]
 ssh_filter_btrbk.sh [-s|--source] [-t|--target] [-d|--delete]
     [-i|--info] [--snapshot] [--send] [--receive]
     [-p|--restrict-path <path>] [-l|--log] [--sudo]