Add a CLI

- Super simple CLI with the ability to read from files and STDIN.
- Add [vendor binary to
`composer.json`](https://getcomposer.org/doc/articles/vendor-binaries.md).
- Add CLI usage to README.

Closes #76.

README.md

@@ -25,6 +25,19 @@ $Parsedown = new Parsedown();
 echo $Parsedown->text('Hello _Parsedown_!'); # prints: <p>Hello <em>Parsedown</em>!</p>
 ```
 
+Or as a command line tool:
+
+``` bash
+# from a file
+./parsedown README.md
+
+# redirect HTML to a file:
+./parsedown README.md > README.html
+
+# or from standard input
+curl https://raw.githubusercontent.com/erusev/parsedown/master/README.md | ./parsedown
+```
+
 More examples in [the wiki](https://github.com/erusev/parsedown/wiki/Usage) and in [this video tutorial](http://youtu.be/wYZBY8DEikI).
 
 ### Questions

composer.json

@@ -14,5 +14,8 @@
     ],
     "autoload": {
         "psr-0": {"Parsedown": ""}
-    }
-}
+    },
+    "bin": [
+    	"parsedown"
+    ]
+}

parsedown

@@ -0,0 +1,24 @@
+#!/usr/bin/env php
+<?php
+
+require(dirname(__FILE__).'/Parsedown.php');
+
+// From a file
+if (isset($argv[1])) {
+
+	if ( ! is_readable($argv[1])) {
+		throw new RuntimeException(sprintf(
+			'Could not read "%s"',
+			$argv[1]
+		));
+	}
+
+	$markdown = file_get_contents($argv[1]);
+} else {
+	// From standard input
+	$markdown = file_get_contents('php://stdin');
+}
+
+$Parsedown = new Parsedown();
+
+echo $Parsedown->text($markdown);