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/ulikunitz/xz/crc.go

@@ -0,0 +1,54 @@
+// Copyright 2014-2017 Ulrich Kunitz. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xz
+
+import (
+	"hash"
+	"hash/crc32"
+	"hash/crc64"
+)
+
+// crc32Hash implements the hash.Hash32 interface with Sum returning the
+// crc32 value in little-endian encoding.
+type crc32Hash struct {
+	hash.Hash32
+}
+
+// Sum returns the crc32 value as little endian.
+func (h crc32Hash) Sum(b []byte) []byte {
+	p := make([]byte, 4)
+	putUint32LE(p, h.Hash32.Sum32())
+	b = append(b, p...)
+	return b
+}
+
+// newCRC32 returns a CRC-32 hash that returns the 64-bit value in
+// little-endian encoding using the IEEE polynomial.
+func newCRC32() hash.Hash {
+	return crc32Hash{Hash32: crc32.NewIEEE()}
+}
+
+// crc64Hash implements the Hash64 interface with Sum returning the
+// CRC-64 value in little-endian encoding.
+type crc64Hash struct {
+	hash.Hash64
+}
+
+// Sum returns the CRC-64 value in little-endian encoding.
+func (h crc64Hash) Sum(b []byte) []byte {
+	p := make([]byte, 8)
+	putUint64LE(p, h.Hash64.Sum64())
+	b = append(b, p...)
+	return b
+}
+
+// crc64Table is used to create a CRC-64 hash.
+var crc64Table = crc64.MakeTable(crc64.ECMA)
+
+// newCRC64 returns a CRC-64 hash that returns the 64-bit value in
+// little-endian encoding using the ECMA polynomial.
+func newCRC64() hash.Hash {
+	return crc64Hash{Hash64: crc64.New(crc64Table)}
+}