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/executable.go

@@ -0,0 +1,25 @@
+package internal
+
+import (
+	"log"
+	"os"
+	"sync"
+)
+
+var (
+	executable     string
+	executableOnce sync.Once
+)
+
+func copyExecutable() {
+	if name, err := os.Executable(); err != nil {
+		log.Fatalf("cannot read executable path: %v", err)
+	} else {
+		executable = name
+	}
+}
+
+func MustExecutable() string {
+	executableOnce.Do(copyExecutable)
+	return executable
+}