Implement Base64 read.

src/bytes_base64.rs

@@ -1,3 +1,4 @@
+#![allow(dead_code)]
 use crate::bytes::Bytes;
 use std::str;
 
@@ -33,6 +34,25 @@ impl BytesBase64 {
         )
     }
 
+    pub fn to_bytes(&self) -> Bytes {
+        Bytes(vec![])
+    }
+
+    pub fn from_base64(s: &str) -> BytesBase64 {
+        let mut r: Vec<u8> = Vec::with_capacity(s.len());
+        for c in s.chars() {
+            match c {
+                'A'..='Z' => r.push((c as u8) - ('A' as u8)),
+                'a'..='z' => r.push((c as u8) - ('a' as u8) + 26),
+                '0'..='9' => r.push((c as u8) - ('0' as u8) + 52),
+                '+' => r.push(62),
+                '/' => r.push(63),
+                _ => (),
+            }
+        }
+        BytesBase64(r)
+    }
+
     pub fn to_string(&self) -> String {
         let BytesBase64(digits) = self;
         let mut r: Vec<u8> = digits