doc: convert the remaining legacy syntax

The block conversion changed the bodies of the reference sections but
left every "**Syntax:**" header spelling the line-based format, so each
page opened by teaching the format it then stopped using.  Six files
were missed entirely: runparts, files, capabilities, requirements,
runlevels, and switchroot.

runparts had no block spelling written down anywhere, though the parser
has read `runparts`, `runparts-progress`, and `runparts-sysv` all along.

tty gains a table per variant.  Its three syntax lines carried nine
positional fields between them, which no longer describes anything the
parser accepts.

Fixes #148

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

doc/config/services.md

@@ -1,7 +1,7 @@
 Services
 ========
 
-**Syntax:** `service [LVLS] <COND> /path/to/daemon ARGS -- Optional description`
+**Syntax:** `service NAME { command = "/path/to/daemon ARGS" }`
 
 Service, or daemon, to be monitored and automatically restarted if it
 exits prematurely.  Finit tries to restart services that die, by default