Add go mod, update ftime.

+ Stat_t on Darwin amd64 now uses the same struct fields
  for file times as Lunix, not the BSD ones. I need to
  follow up on this.

go.mod

@@ -0,0 +1,3 @@
+module github.com/kisom/goutils
+
+go 1.13

lib/ftime_bsd.go

@@ -1,4 +1,4 @@
-// +build freebsd darwin netbsd
+// +build freebsd darwin,386 netbsd
 
 package lib