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/runlevels.md

@@ -26,8 +26,16 @@ the lifetime of your system.
 
 Example:
 
-    task [S] /lib/console-setup/console-setup.sh
-    service [S12345] env:-/etc/default/rsyslog rsyslogd -n $RSYSLOGD_ARGS
+    task console-setup {
+        runlevel = "S"
+        command  = "/lib/console-setup/console-setup.sh"
+    }
+
+    service rsyslogd {
+        runlevel = "S12345"
+        envfile  = "-/etc/default/rsyslog"
+        command  = "rsyslogd -n $RSYSLOGD_ARGS"
+    }
 
 When bootstrap has completed, Finit moves to runlevel 2.  This can be
 changed in `/etc/finit.conf` using the `runlevel N` directive, or by a