[feature] S3 support (#674)

* feat: vendor minio client

* feat: introduce storage package with s3 support

* feat: serve s3 files directly

this saves a lot of bandwith as the files are fetched from the object
store directly

* fix: use explicit local storage in tests

* feat: integrate s3 storage with the main server

* fix: add s3 config to cli tests

* docs: explicitly set values in example config

also adds license header to the storage package

* fix: use better http status code on s3 redirect

HTTP 302 Found is the best fit, as it signifies that the resource
requested was found but not under its presumed URL

307/TemporaryRedirect would mean that this resource is usually located
here, not in this case

303/SeeOther indicates that the redirection does not link to the
requested resource but to another page

* refactor: use context in storage driver interface

vendor/github.com/minio/md5-simd/md5-util_amd64.go

@@ -0,0 +1,70 @@
+// Copyright (c) 2020 MinIO Inc. All rights reserved.
+// Use of this source code is governed by a license that can be
+// found in the LICENSE file.
+
+package md5simd
+
+import (
+	"sort"
+)
+
+// Helper struct for sorting blocks based on length
+type lane struct {
+	len uint
+	pos uint
+}
+
+// Helper struct for generating number of rounds in combination with mask for valid lanes
+type maskRounds struct {
+	mask   uint64
+	rounds uint64
+}
+
+func generateMaskAndRounds8(input [8][]byte, mr *[8]maskRounds) (rounds int) {
+	// Sort on blocks length small to large
+	var sorted [8]lane
+	for c, inpt := range input {
+		sorted[c] = lane{uint(len(inpt)), uint(c)}
+	}
+	sort.Slice(sorted[:], func(i, j int) bool { return sorted[i].len < sorted[j].len })
+
+	// Create mask array including 'rounds' (of processing blocks of 64 bytes) between masks
+	m, round := uint64(0xff), uint64(0)
+
+	for _, s := range sorted {
+		if s.len > 0 {
+			if uint64(s.len)>>6 > round {
+				mr[rounds] = maskRounds{m, (uint64(s.len) >> 6) - round}
+				rounds++
+			}
+			round = uint64(s.len) >> 6
+		}
+		m = m & ^(1 << uint(s.pos))
+	}
+	return
+}
+
+func generateMaskAndRounds16(input [16][]byte, mr *[16]maskRounds) (rounds int) {
+
+	// Sort on blocks length small to large
+	var sorted [16]lane
+	for c, inpt := range input {
+		sorted[c] = lane{uint(len(inpt)), uint(c)}
+	}
+	sort.Slice(sorted[:], func(i, j int) bool { return sorted[i].len < sorted[j].len })
+
+	// Create mask array including 'rounds' (of processing blocks of 64 bytes) between masks
+	m, round := uint64(0xffff), uint64(0)
+
+	for _, s := range sorted {
+		if s.len > 0 {
+			if uint64(s.len)>>6 > round {
+				mr[rounds] = maskRounds{m, (uint64(s.len) >> 6) - round}
+				rounds++
+			}
+			round = uint64(s.len) >> 6
+		}
+		m = m & ^(1 << uint(s.pos))
+	}
+	return
+}