Process astral characters correctly

According to YAML 1.2 spec, #xD800-#xDFFF unicode range is considered
non-printables. But unicode range #x10000-#x10FFFF, represented
in UTF-16 by the same characters is not.

NOTE: Non-printable characters are still allowed in quoted scalars,
added a pending test for this case.

Fixes: #191

lib/js-yaml/loader.js

@@ -23,7 +23,7 @@ var CHOMPING_STRIP = 2;
 var CHOMPING_KEEP  = 3;
 
 
-var PATTERN_NON_PRINTABLE         = /[\x00-\x08\x0B\x0C\x0E-\x1F\x7F-\x84\x86-\x9F\uD800-\uDFFF\uFFFE\uFFFF]/;
+var PATTERN_NON_PRINTABLE         = /[\x00-\x08\x0B\x0C\x0E-\x1F\x7F-\x84\x86-\x9F\uFFFE\uFFFF]|[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?:[^\uD800-\uDBFF]|^)[\uDC00-\uDFFF]/;
 var PATTERN_NON_ASCII_LINE_BREAKS = /[\x85\u2028\u2029]/;
 var PATTERN_FLOW_INDICATORS       = /[,\[\]\{\}]/;
 var PATTERN_TAG_HANDLE            = /^(?:!|!!|![a-z\-]+!)$/i;

test/units/character-set.js

@@ -0,0 +1,25 @@
+'use strict';
+
+
+var assert = require('assert');
+var yaml = require('../../');
+
+
+test('Allow astral characters', function () {
+  assert.deepEqual(yaml.load('𝑘𝑒𝑦: 𝑣𝑎𝑙𝑢𝑒'), { '𝑘𝑒𝑦': '𝑣𝑎𝑙𝑢𝑒' });
+});
+
+test('Forbid non-printable characters', function () {
+  assert.throws(function () { yaml.load('\x01'); }, yaml.YAMLException);
+  assert.throws(function () { yaml.load('\x7f'); }, yaml.YAMLException);
+  assert.throws(function () { yaml.load('\x9f'); }, yaml.YAMLException);
+});
+
+test('Forbid lone surrogates', function () {
+  assert.throws(function () { yaml.load('\udc00\ud800'); }, yaml.YAMLException);
+});
+
+test.skip('Allow non-printable characters inside quoted scalars', function () {
+  assert.strictEqual(yaml.load('"\x7f\x9f\udc00\ud800"'), '\x7f\x9f\udc00\ud800');
+});
+