add build targets

cmd/beornextract/BUILD

@@ -12,6 +12,6 @@ alias(
 go_library(
     name = "beornextract_lib",
     srcs = ["main.go"],
-    importpath = "github.com/squk/lotr/beornextract",
+    importpath = "github.com/squk/lotr/cmd/beornextract",
     deps = ["@com_github_davecgh_go_spew//spew"],
 )