fmsg: implement suspend in writer

This removes the requirement to call fmsg.Exit on every exit path, and enables direct use of the "log" package. However, fmsg.BeforeExit is still encouraged when possible to catch exit on suspended output.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/system/link.go

@@ -28,18 +28,18 @@ type Hardlink struct {
 func (l *Hardlink) Type() Enablement { return l.et }
 
 func (l *Hardlink) apply(_ *I) error {
-	fmsg.VPrintln("linking ", l)
+	fmsg.Verbose("linking ", l)
 	return fmsg.WrapErrorSuffix(os.Link(l.src, l.dst),
 		fmt.Sprintf("cannot link %q:", l.dst))
 }
 
 func (l *Hardlink) revert(_ *I, ec *Criteria) error {
 	if ec.hasType(l) {
-		fmsg.VPrintf("removing hard link %q", l.dst)
+		fmsg.Verbosef("removing hard link %q", l.dst)
 		return fmsg.WrapErrorSuffix(os.Remove(l.dst),
 			fmt.Sprintf("cannot remove hard link %q:", l.dst))
 	} else {
-		fmsg.VPrintf("skipping hard link %q", l.dst)
+		fmsg.Verbosef("skipping hard link %q", l.dst)
 		return nil
 	}
 }