remove __proto__ from EncodedData and family

EncodedData was setting "converter" and "_encoding" by setting them on the
prototype of the object. This was probably done to enable overriding these
functions. However, overriding was never actually used anywhere, and setting
the __proto__ is deprecated. So I have remove all instances of setting
__proto__ for EncodedData-ish classes, and instead just set "convert" and
"_encoding" on the object directly.

lib/SIN.js

@@ -8,7 +8,7 @@ function SIN(type, payload) {
     return;
   };
   this.data = new Buffer(1 + 1 + payload.length);
-  this.__proto__ = this.encodings['binary'];
+  this.encoding('binary');
   this.prefix(0x0F); // SIN magic number, in numberspace
   this.type(type);
   this.payload(payload);

util/EncodedData.js

@@ -8,9 +8,14 @@ var base58 = require('../lib/Base58').base58Check;
 function EncodedData(data, encoding) {
   this.data = data;
   if (!encoding && (typeof data == 'string')) {
-    this.__proto__ = this.encodings['base58'];
+    encoding = 'base58';
+    this.converters = this.encodings[encoding].converters;
+    this._encoding = this.encodings[encoding]._encoding;
   } else {
-    this.__proto__ = this.encodings[encoding || 'binary'];
+    if (typeof this.encodings[encoding] === 'undefined')
+      encoding = 'binary';
+    this.converters = this.encodings['binary'].converters;
+    this._encoding = this.encodings['binary']._encoding;
   }
 };
 
@@ -18,7 +23,8 @@ function EncodedData(data, encoding) {
 EncodedData.prototype.encoding = function(encoding) {
   if (encoding && (encoding != this._encoding)) {
     this.data = this.as(encoding);
-    this.__proto__ = this.encodings[encoding];
+    this.converters = this.encodings[encoding].converters;
+    this._encoding = this.encodings[encoding]._encoding;
   }
   return this._encoding;
 };

util/VersionedData.js

@@ -9,7 +9,7 @@ function VersionedData(version, payload) {
     return;
   };
   this.data = new Buffer(payload.length + 1);
-  this.__proto__ = this.encodings['binary'];
+  this.encoding('binary');
   this.version(version);
   this.payload(payload);
 };