vendor the dependencies

There is a discrepancy of behavior of `github.com/urfave/cli` between
using go1.12 and go1.15, when the dependency is not present as vendored
source. Now this builds fine with go1.12

There are users of tar-split as a package. It is the hope that by adding
this vendored source it does not impact them depending on tar-split
itself.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/sirupsen/logrus/buffer_pool.go

@@ -0,0 +1,52 @@
+package logrus
+
+import (
+	"bytes"
+	"sync"
+)
+
+var (
+	bufferPool BufferPool
+)
+
+type BufferPool interface {
+	Put(*bytes.Buffer)
+	Get() *bytes.Buffer
+}
+
+type defaultPool struct {
+	pool *sync.Pool
+}
+
+func (p *defaultPool) Put(buf *bytes.Buffer) {
+	p.pool.Put(buf)
+}
+
+func (p *defaultPool) Get() *bytes.Buffer {
+	return p.pool.Get().(*bytes.Buffer)
+}
+
+func getBuffer() *bytes.Buffer {
+	return bufferPool.Get()
+}
+
+func putBuffer(buf *bytes.Buffer) {
+	buf.Reset()
+	bufferPool.Put(buf)
+}
+
+// SetBufferPool allows to replace the default logrus buffer pool
+// to better meets the specific needs of an application.
+func SetBufferPool(bp BufferPool) {
+	bufferPool = bp
+}
+
+func init() {
+	SetBufferPool(&defaultPool{
+		pool: &sync.Pool{
+			New: func() interface{} {
+				return new(bytes.Buffer)
+			},
+		},
+	})
+}