Support backslash based escaping for placeholders

The simpleParse method of parser, which get invoked if message contains
only placeholders, was not supporting escaped placeholders(\\$10)

The light weight versio of jquery.i18n when parser.js not included
also has the same fix now.

Add support for that and add tests.
Updated the documentation in README.md too

Fixes issue #74

Author: santhoshtr

README.md

@@ -313,7 +313,12 @@ var message = "Welcome, $1";
 $.i18n(message, 'Alice'); // This gives "Welcome, Alice"
 ```
 
-
+To escape the $ sign, use double blackslash in json file. Example:
+```javascript
+{
+	"messageKey": "Price of {{PLURAL:$1|an item|$1 items}} is $2, you get \\$2 discount."
+}
+```
 ## Plurals
 
 To make the syntax of sentence correct, plural forms are required. jquery.i18n support plural forms in the message using the syntax `{{PLURAL:$1|pluralform1|pluralform2|...}}`

src/jquery.i18n.js

@@ -260,9 +260,15 @@
 	$.i18n.parser = {
 		// The default parser only handles variable substitution
 		parse: function ( message, parameters ) {
-			return message.replace( /\$(\d+)/g, function ( str, match ) {
-				var index = parseInt( match, 10 ) - 1;
-				return parameters[ index ] !== undefined ? parameters[ index ] : '$' + match;
+			return message.replace( /(\\?\$\d+)/g, function ( str, match ) {
+				var index;
+
+				if ( match[ 0 ] === '\\' ) {
+					// Escaped.
+					return match.slice( 1 );
+				}
+				index = parseInt( match.slice( 1 ), 10 ) - 1;
+				return parameters[index] !== undefined ? parameters[index] : match;
 			} );
 		},
 		emitter: {}

src/jquery.i18n.parser.js

@@ -27,10 +27,15 @@
 		constructor: MessageParser,
 
 		simpleParse: function ( message, parameters ) {
-			return message.replace( /\$(\d+)/g, function ( str, match ) {
-				var index = parseInt( match, 10 ) - 1;
+			return message.replace( /(\\?\$\d+)/g, function ( str, match ) {
+				var index;
 
-				return parameters[ index ] !== undefined ? parameters[ index ] : '$' + match;
+				if ( match[ 0 ] === '\\' ) {
+					// Escaped.
+					return match.slice( 1 );
+				}
+				index = parseInt( match.slice( 1 ), 10 ) - 1;
+				return parameters[index] !== undefined ? parameters[index] : match;
 			} );
 		},
 

test/i18n/test-en.json

@@ -1,5 +1,6 @@
 {
 	"message_1": "ONE",
 	"message_2": "TWO",
-	"message_3": "THREE"
+	"message_3": "THREE",
+	"message_4": "Total \\$1 of \\$1500"
 }

test/jquery.i18n.test.js

@@ -34,7 +34,7 @@
 		}
 	} );
 
-	QUnit.test( 'Message parse tests (en)', 14, function ( assert ) {
+	QUnit.test( 'Message parse tests (en)', 16, function ( assert ) {
 		var pluralAndGenderMessage,
 			pluralAndGenderMessageWithLessParaMS,
 			pluralAndGenderMessageWithCase,
@@ -49,13 +49,16 @@
 			QUnit.start();
 			assert.strictEqual( i18n.locale, 'en', 'Locale is English' );
 			assert.strictEqual( $.i18n( 'message_1' ), 'ONE', 'Simple message' );
+			assert.strictEqual( $.i18n( 'message_4', 5 ), 'Total $1 of $1500', 'Parameter replacement escaped' );
 		} );
 		assert.strictEqual(
 			$.i18n( 'This message key does not exist' ),
 			'This message key does not exist',
 			'This message key does not exist'
 		);
 		assert.strictEqual( $.i18n( 'Hello $1', 'Bob' ), 'Hello Bob', 'Parameter replacement' );
+		assert.strictEqual(  $.i18n( 'Price of {{PLURAL:$1|an item|$1 items}} is $2, you get \\$2 discount', 5, 2000 ),
+			'Price of 5 items is 2000, you get $2 discount', 'Parameter replacement with dollar sign escaped, not parsed using simplePaser' );
 		pluralAndGenderMessage = '$1 has $2 {{plural:$2|kitten|kittens}}. ' +
 			'{{gender:$3|He|She}} loves to play with {{plural:$2|it|them}}.';
 		pluralAndGenderMessageWithLessParaMS = '$1 has $2 {{plural:$2|kitten}}. ' +