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/bits.go

@@ -0,0 +1,74 @@
+// 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 (
+	"errors"
+	"io"
+)
+
+// putUint32LE puts the little-endian representation of x into the first
+// four bytes of p.
+func putUint32LE(p []byte, x uint32) {
+	p[0] = byte(x)
+	p[1] = byte(x >> 8)
+	p[2] = byte(x >> 16)
+	p[3] = byte(x >> 24)
+}
+
+// putUint64LE puts the little-endian representation of x into the first
+// eight bytes of p.
+func putUint64LE(p []byte, x uint64) {
+	p[0] = byte(x)
+	p[1] = byte(x >> 8)
+	p[2] = byte(x >> 16)
+	p[3] = byte(x >> 24)
+	p[4] = byte(x >> 32)
+	p[5] = byte(x >> 40)
+	p[6] = byte(x >> 48)
+	p[7] = byte(x >> 56)
+}
+
+// uint32LE converts a little endian representation to an uint32 value.
+func uint32LE(p []byte) uint32 {
+	return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 |
+		uint32(p[3])<<24
+}
+
+// putUvarint puts a uvarint representation of x into the byte slice.
+func putUvarint(p []byte, x uint64) int {
+	i := 0
+	for x >= 0x80 {
+		p[i] = byte(x) | 0x80
+		x >>= 7
+		i++
+	}
+	p[i] = byte(x)
+	return i + 1
+}
+
+// errOverflow indicates an overflow of the 64-bit unsigned integer.
+var errOverflowU64 = errors.New("xz: uvarint overflows 64-bit unsigned integer")
+
+// readUvarint reads a uvarint from the given byte reader.
+func readUvarint(r io.ByteReader) (x uint64, n int, err error) {
+	var s uint
+	i := 0
+	for {
+		b, err := r.ReadByte()
+		if err != nil {
+			return x, i, err
+		}
+		i++
+		if b < 0x80 {
+			if i > 10 || i == 10 && b > 1 {
+				return x, i, errOverflowU64
+			}
+			return x | uint64(b)<<s, i, nil
+		}
+		x |= uint64(b&0x7f) << s
+		s += 7
+	}
+}