Use PSR-4 and autoload-dev

- PSR-4 is the successor of PSR-0. PSR-0 is deprecated now.
  The provided autoloader does not respect the underscore rule from PSR-0 anyway.
- `autoload-dev` is a feature of Composer to dump additional namespaces in the autoloader
  when dev dependencies are being installed. This way there is no need to have a separate bootstrap file for PHPUnit.

README.md

@@ -149,7 +149,7 @@ Unit Tests
 
 Setup the test suite using Composer:
 
-    $ composer install --dev
+    $ composer install
 
 Run it using PHPUnit:
 

composer.json

@@ -14,7 +14,10 @@
         "php": ">=5.3.0"
     },
     "autoload": {
-        "psr-0": { "EmailReplyParser": "src/" }
+        "psr-4": { "EmailReplyParser\\": "src/EmailReplyParser" }
+    },
+    "autoload-dev": {
+        "psr-4": { "EmailReplyParser\\Tests\\": "tests/EmailReplyParser/Tests" }
     },
     "extra": {
         "branch-alias": {

phpunit.xml.dist

@@ -8,7 +8,7 @@
     processIsolation="false"
     stopOnFailure="false"
     syntaxCheck="false"
-    bootstrap="tests/bootstrap.php"
+    bootstrap="vendor/autoload.php"
     >
     <testsuites>
         <testsuite name="EmailReplyParser Test Suite">