Add golangci-lint (#502)

Initial part of #435

vendor/github.com/shazow/go-diff/difflib/differ.go

@@ -0,0 +1,39 @@
+// This package implements the diff.Differ interface using github.com/mb0/diff as a backend.
+package difflib
+
+import (
+	"io"
+	"io/ioutil"
+
+	"github.com/pmezard/go-difflib/difflib"
+)
+
+type differ struct{}
+
+// New returns an implementation of diff.Differ using mb0diff as the backend.
+func New() *differ {
+	return &differ{}
+}
+
+// Diff consumes the entire reader streams into memory before generating a diff
+// which then gets filled into the buffer. This implementation stores and
+// manipulates all three values in memory.
+func (diff *differ) Diff(out io.Writer, a io.ReadSeeker, b io.ReadSeeker) error {
+	var src, dst []byte
+	var err error
+
+	if src, err = ioutil.ReadAll(a); err != nil {
+		return err
+	}
+	if dst, err = ioutil.ReadAll(b); err != nil {
+		return err
+	}
+
+	d := difflib.UnifiedDiff{
+		A:       difflib.SplitLines(string(src)),
+		B:       difflib.SplitLines(string(dst)),
+		Context: 3,
+	}
+
+	return difflib.WriteUnifiedDiff(out, d)
+}