Improve AsciiDoc compatibility

I need two renderers to work: hswg/libasciidoc and asciidoctor
in man page mode (and ideally in HTML as well).  That should be
covered now.

The triple-plus thing was the first thing that showed good results,
after trying backslashes, single-plus quoting and [] after ://.

The change of the source code block kind could be considered as
unification.  I'm combining tabs with spaces within one document
though, and I should get rid of the tabs in the rest of it then...

json-rpc-shell.adoc

@@ -15,7 +15,7 @@ Synopsis
 Description
 -----------
 The _ENDPOINT_ must be either an HTTP or a WebSocket URL, with or without TLS
-(i.e. one of the _http://_, _https://_, _ws://_, _wss://_ schemas).
+(i.e. one of the _+++http+++://_, _+++https+++://_, _ws://_, _wss://_ schemas).
 
 *json-rpc-shell* will use it to send any JSON-RPC 2.0 requests you enter on its
 command line. The server's response will be parsed and validated, stripping it
@@ -133,7 +133,6 @@ distribution of this program (public services are hard to find):
 
 Pretty-printing and Manual IDs
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-```
  $ json-rpc-shell -p ws://localhost:1234
  json-rpc> date 1
  {
@@ -144,29 +143,24 @@ json-rpc> date 1
    "minutes": 23,
    "seconds": 51
  }
-```
 
 Notification With a Parameter
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Notifications never produce a response, not even when the method is not known
 to the server:
 
-```
  $ json-rpc-shell ws://localhost:1234
  json-rpc> notify {"events": ["conquest", "war", "famine", "death"]}
  [Notification]
-```
 
 Piping In and Out
 ~~~~~~~~~~~~~~~~~
 GNU Readline always repeats the prompt, which makes this a bit less useful
 for invoking from other programs:
 
-```
  $ echo 'ping | jq ascii_upcase' | json-rpc-shell -a ws://localhost:1234
  json-rpc> ping | jq ascii_upcase
  "PONG"
-```
 
 Reporting Bugs
 --------------