Refactor repository layout and convert build system to Mage.

This commit implements a massive refactor of the repository, and
moves the build system over to use Mage (magefile.org) which should
allow seamless building across multiple platforms.

tools/vendor/mvdan.cc/unparam/main.go

@@ -6,24 +6,34 @@ package main // import "mvdan.cc/unparam"
 import (
 	"flag"
 	"fmt"
+	"go/build"
 	"os"
 
+	"golang.org/x/tools/go/buildutil"
+
 	"mvdan.cc/unparam/check"
 )
 
 var (
+	algo     = flag.String("algo", "cha", `call graph construction algorithm (cha, rta).
+in general, use cha for libraries, and rta for programs with main packages.`)
 	tests    = flag.Bool("tests", true, "include tests")
 	exported = flag.Bool("exported", false, "inspect exported functions")
 	debug    = flag.Bool("debug", false, "debug prints")
 )
 
+func init() {
+	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags",
+		buildutil.TagsFlagDoc)
+}
+
 func main() {
 	flag.Usage = func() {
 		fmt.Fprintln(os.Stderr, "usage: unparam [flags] [package ...]")
 		flag.PrintDefaults()
 	}
 	flag.Parse()
-	warns, err := check.UnusedParams(*tests, *exported, *debug, flag.Args()...)
+	warns, err := check.UnusedParams(*tests, *algo, *exported, *debug, flag.Args()...)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)