crypto: move merkle tree into the hash package

It's all about hashes, so it makes sense putting it there.

pkg/crypto/hash/merkle_tree_test.go

@@ -0,0 +1,29 @@
+package hash
+
+import (
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/util"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestComputeMerkleTree(t *testing.T) {
+	rawHashes := []string{
+		"fb5bd72b2d6792d75dc2f1084ffa9e9f70ca85543c717a6b13d9959b452a57d6",
+		"c56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b",
+		"602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7",
+		"3631f66024ca6f5b033d7e0809eb993443374830025af904fb51b0334f127cda",
+	}
+
+	hashes := make([]util.Uint256, len(rawHashes))
+	for i, str := range rawHashes {
+		hash, _ := util.Uint256DecodeStringLE(str)
+		hashes[i] = hash
+	}
+
+	merkle, err := NewMerkleTree(hashes)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, "803ff4abe3ea6533bcc0be574efa02f83ae8fdc651c879056b0d9be336c01bf4", merkle.Root().StringLE())
+}