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/service-env.md

@@ -13,7 +13,12 @@ file `/etc/default/foo`.  Like this:
 
 * `/etc/finit.conf`:
 
-        service [2345] env:-/etc/default/foo foo -n $FOO_OPTIONS -- Example foo daemon
+        service foo {
+            description = "Example foo daemon"
+            runlevel    = "2345"
+            envfile     = "-/etc/default/foo"
+            command     = "foo -n $FOO_OPTIONS"
+        }
 
 Here the service `foo` is started with `-n`, to make sure it runs in the
 foreground, and the with the options found in the environment file.  With
@@ -22,6 +27,8 @@ the `ps` command we can see that the process is started with:
     foo -n --extra-arg=bar -s -x
 
 > [!NOTE]
-> The leading `-` in `env:` determines if Finit should treat a missing
-> environment file as blocking the start of the service or not.  When
-> `-` is used, a missing environment file does *not* block the start.
+> The leading `-` on `envfile` determines if Finit should treat a
+> missing environment file as blocking the start of the service or not.
+> When `-` is used, a missing environment file does *not* block the
+> start.  The same mark works on `command`, where it means carry on if
+> the binary is missing.