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/logging.md

@@ -38,12 +38,19 @@ Log rotation is controlled using the global `log` setting.
 
 **Example:**
 
-    service log:prio:user.warn,tag:ntpd /sbin/ntpd pool.ntp.org -- NTP daemon
+    service ntpd {
+        description = "NTP daemon"
+        log {
+            priority = "user.warn"
+            identity = "ntpd"
+        }
+        command = "/sbin/ntpd pool.ntp.org"
+    }
 
 Output Buffering
 ----------------
 
-When using the `log` directive, Finit redirects the service's stdout and
+When using the `log` block, Finit redirects the service's stdout and
 stderr to a pipe connected to a logger process.  Programs detect this as
 non-interactive output (i.e., `isatty()` returns false) and typically
 switch from line-buffered to fully-buffered mode.
@@ -53,7 +60,11 @@ directly, so this is rarely an issue.  However, if a service's log
 messages appear delayed or batched, you can force line-buffered output
 by wrapping the command with `stdbuf`:
 
-    service log /usr/bin/stdbuf -oL /path/to/command -- My service
+    service myservice {
+        description = "My service"
+        log { }
+        command = "/usr/bin/stdbuf -oL /path/to/command"
+    }
 
 The `-oL` option forces line-buffered output, and `-o0` forces unbuffered
 output.  See `stdbuf(1)` for details.