doc: convert the documentation to the block format

The syntax overview no longer describes a line-based format, since that
is not what the rest of the documentation shows.  It now covers the
grammar, the two naming conventions, the nine aliases, and the leading
'-' on a path, and it says plainly that both formats are still read and
told apart per file by content.  Without that, a reader with an
existing configuration is left wondering what happened to it.

service-opts.md was a list of modifiers to place between a directive
and its command, so it needed rewriting rather than translating: there
are no positions left to describe.  It is now grouped by what the
settings do.

conditions.md needed correcting.  It presented '!' as a condition
prefix alongside '~'.  It is neither a condition nor a negation, it is
a flag on the block that means one thing on a service and another on a
run or task, so it is spelled reload-signal and required here, and the
page maps the old form to both.

Two things the pages claimed are not true.  The kill delay range is
1-300, not 1-60, and stop and reload scripts are no longer run without
a timeout.

ChangeLog.md keeps its line-based examples.  Those sit in historical
release entries, and rewriting them in a syntax that did not exist at
the time would misdate the format.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/config/rescue.md

@@ -48,7 +48,10 @@ system administrator.
 The bundled default `rescue.conf` contains nothing more than:
 
     runlevel 1
-    tty [12345] rescue
+    tty rescue {
+        runlevel = "12345"
+        rescue   = true
+    }
 
 The `tty` has the `rescue` option set, which works similar to the board
 bring-up tty option `notty`.  The major difference being that `sulogin`
@@ -57,6 +60,9 @@ is started to query for root/admin password.  If `sulogin` is not found,
 
 If Finit cannot find `/lib/finit/rescue.conf` it defaults to:
 
-    tty [12345] rescue
+    tty rescue {
+        runlevel = "12345"
+        rescue   = true
+    }
 
 There is no way to exit the *fallback* rescue mode.