TUN-4063: Cleanup dependencies between packages.

- Move packages the provide generic functionality (such as config) from `cmd` subtree to top level.
- Remove all dependencies on `cmd` subtree from top level packages.
- Consolidate all code dealing with token generation and transfer to a single cohesive package.

origin/pool.go

@@ -0,0 +1,29 @@
+package origin
+
+import (
+	"sync"
+)
+
+type bufferPool struct {
+	// A bufferPool must not be copied after first use.
+	// https://golang.org/pkg/sync/#Pool
+	buffers sync.Pool
+}
+
+func newBufferPool(bufferSize int) *bufferPool {
+	return &bufferPool{
+		buffers: sync.Pool{
+			New: func() interface{} {
+				return make([]byte, bufferSize)
+			},
+		},
+	}
+}
+
+func (p *bufferPool) Get() []byte {
+	return p.buffers.Get().([]byte)
+}
+
+func (p *bufferPool) Put(buf []byte) {
+	p.buffers.Put(buf)
+}