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.

vendor/github.com/magefile/mage/target/target.go

@@ -0,0 +1,122 @@
+package target
+
+import (
+	"os"
+	"path/filepath"
+	"time"
+)
+
+// Path reports if any of the sources have been modified more recently
+// than the destination.  Path does not descend into directories, it literally
+// just checks the modtime of each thing you pass to it.
+func Path(dst string, sources ...string) (bool, error) {
+	stat, err := os.Stat(dst)
+	if err != nil {
+		return false, err
+	}
+	srcTime := stat.ModTime()
+	dt, err := loadTargets(sources)
+	if err != nil {
+		return false, err
+	}
+	t := dt.modTime()
+	if t.After(srcTime) {
+		return true, nil
+	}
+	return false, nil
+}
+
+// Dir reports whether any of the sources have been modified
+// more recently than the destination.  If a source or destination is
+// a directory, modtimes of files under those directories are compared
+// instead.
+func Dir(dst string, sources ...string) (bool, error) {
+	stat, err := os.Stat(dst)
+	if err != nil {
+		return false, err
+	}
+	srcTime := stat.ModTime()
+	if stat.IsDir() {
+		srcTime, err = calDirModTimeRecursive(stat)
+		if err != nil {
+			return false, err
+		}
+	}
+	dt, err := loadTargets(sources)
+	if err != nil {
+		return false, err
+	}
+	t, err := dt.modTimeDir()
+	if err != nil {
+		return false, err
+	}
+	if t.After(srcTime) {
+		return true, nil
+	}
+	return false, nil
+}
+
+func calDirModTimeRecursive(dir os.FileInfo) (time.Time, error) {
+	t := dir.ModTime()
+	ferr := filepath.Walk(dir.Name(), func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.ModTime().After(t) {
+			t = info.ModTime()
+		}
+		return nil
+	})
+	if ferr != nil {
+		return time.Time{}, ferr
+	}
+	return t, nil
+}
+
+type depTargets struct {
+	src    []os.FileInfo
+	hasdir bool
+	latest time.Time
+}
+
+func loadTargets(targets []string) (*depTargets, error) {
+	d := &depTargets{}
+	for _, v := range targets {
+		stat, err := os.Stat(v)
+		if err != nil {
+			return nil, err
+		}
+		if stat.IsDir() {
+			d.hasdir = true
+		}
+		d.src = append(d.src, stat)
+		if stat.ModTime().After(d.latest) {
+			d.latest = stat.ModTime()
+		}
+	}
+	return d, nil
+}
+
+func (d *depTargets) modTime() time.Time {
+	return d.latest
+}
+
+func (d *depTargets) modTimeDir() (time.Time, error) {
+	if !d.hasdir {
+		return d.latest, nil
+	}
+	var err error
+	for _, i := range d.src {
+		t := i.ModTime()
+		if i.IsDir() {
+			t, err = calDirModTimeRecursive(i)
+			if err != nil {
+				return time.Time{}, err
+			}
+		}
+		if t.After(d.latest) {
+			d.latest = t
+		}
+	}
+	return d.latest, nil
+}