Add Standard Markdown testsuite.

You could run the Parsedown testsuite only with:
    phpunit --testsuite ParsedownTests

And you could run the Standard Markdown one with:
    phpunit --testsuite StandardMarkdown

See more at http://standardmarkdown.com/

.travis.yml

@@ -7,4 +7,5 @@ php:
   - 5.3
   - 5.2
   - hhvm
-  
+
+before_script: curl -sS https://raw.githubusercontent.com/jgm/stmd/master/spec.txt>test/standard-markdown/spec.txt

phpunit.xml.dist

@@ -1,8 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit bootstrap="test/bootstrap.php" colors="true">
 	<testsuites>
-		<testsuite>
-			<file>test/Test.php</file>
+        <testsuite name="ParsedownTests">
+            <file>test/Test.php</file>
+        </testsuite>
+		<testsuite name="StandardMarkdown">
+			<file>test/standard-markdown/StandardMarkdownTest.php</file>
 		</testsuite>
 	</testsuites>
-</phpunit>
+</phpunit>

test/standard-markdown/.gitignore

@@ -0,0 +1 @@
+spec.txt

test/standard-markdown/StandardMarkdownTest.php

@@ -0,0 +1,60 @@
+<?php
+
+class StandardMarkdownTest extends PHPUnit_Framework_TestCase
+{
+    const SPEC_FILEPATH = 'spec.txt';
+
+    const SPEC_URL = 'https://raw.githubusercontent.com/jgm/stmd/master/spec.txt';
+
+    public function getStandardMarkdownRules()
+    {
+        if (is_file(self::SPEC_FILEPATH) and is_readable(self::SPEC_FILEPATH)) {
+            $spec = file_get_contents(self::SPEC_FILEPATH);
+        } else {
+            $spec = file_get_contents(self::SPEC_URL);
+        }
+
+        $tests = array();
+        $testsCount = 0;
+        $currentSection = '';
+
+        $spec = preg_replace('/^<!-- END TESTS -->(.|[\n])*/m', '', $spec);
+
+        preg_replace_callback(
+            '/^\.\n([\s\S]*?)^\.\n([\s\S]*?)^\.$|^#{1,6} *(.*)$/m',
+            function($matches) use (&$tests, &$currentSection, &$testsCount) {
+                if (isset($matches[3]) and $matches[3]) {
+                    $currentSection = $matches[3];
+                } else {
+                    $testsCount++;
+                    $markdown = preg_replace('/→/', "\t", $matches[1]);
+                    $tests []= array(
+                        $markdown,       // markdown
+                        $matches[2],     // html
+                        $currentSection, // section
+                        $testsCount,     // number
+                    );
+                }
+            },
+            $spec
+        );
+
+        return $tests;
+    }
+
+    /**
+     * @dataProvider getStandardMarkdownRules
+     */
+    public function testAgainstStandardMarkdown($markdown, $expectedHtml, $section, $number)
+    {
+        $parsedown = new Parsedown();
+
+        $actualHtml = $parsedown->text($markdown);
+
+        // Trim for better compatibility of the HTML output
+        $actualHtml = trim($actualHtml);
+        $expectedHtml = trim($expectedHtml);
+
+        $this->assertEquals($expectedHtml, $actualHtml);
+    }
+}