Add link metadata fetching package

vendor/github.com/golang-commonmark/markdown/linkify/charset.go

@@ -0,0 +1,50 @@
+// Copyright 2015 The Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package linkify
+
+import "unicode"
+
+var (
+	trigger    [256]bool
+	unreserved [256]bool
+	subdelims  [256]bool
+	emailcs    [256]bool
+	basicPunct [256]bool
+)
+
+func init() {
+	for _, b := range "-._~" {
+		unreserved[b] = true
+	}
+	for _, b := range "!$&'()*+,;=" {
+		subdelims[b] = true
+	}
+	for _, b := range "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!#$%&'*+/=?^_`{|}~-" {
+		emailcs[b] = true
+	}
+	for _, b := range ".,?!;:" {
+		basicPunct[b] = true
+	}
+}
+
+func isAllowedInEmail(r rune) bool {
+	return r < 0x7f && emailcs[r]
+}
+
+func isLetterOrDigit(r rune) bool {
+	return unicode.In(r, unicode.Letter, unicode.Digit)
+}
+
+func isPunctOrSpaceOrControl(r rune) bool {
+	return r == '<' || r == '>' || unicode.In(r, unicode.Punct, unicode.Space, unicode.Cc)
+}
+
+func isUnreserved(r rune) bool {
+	return (r < 0x7f && unreserved[r]) || isLetterOrDigit(r)
+}
+
+func isSubDelimiter(r rune) bool {
+	return r < 0x7f && subdelims[r]
+}