Standardize minimum PHP version declaration

CONTRIBUTE.md

@@ -16,7 +16,7 @@ The project generally follows the [PSR-4 coding standards](http://www.php-fig.or
 Regarding the architecture, this project is heavily based on ZF2 architecture and philosophy, so the ZF2 documentation
 will also be a valuable source of information.
 
-Since the system requires PHP 5.4+, everyone is encouraged to use all the new features that version has to offer.
+Since the system requires PHP 5.6+, everyone is encouraged to use all the new features that version has to offer.
 
 ## License
 

public/index.php

@@ -1,15 +1,6 @@
 <?php
 /**
- * Welcome to the famous*, beloved*, highly respected*
- *
- * ep-3 Bookingsystem
- *
- * (c) 2018 Tobias Krebs
- *
- * Website: http://bs.hbsys.de/
- * License: MIT
- *
- * (* Not yet, but maybe some day ...)
+ * ep-3 Bookingsystem Entry Point
  */
 
 ob_start();
@@ -19,8 +10,8 @@
 /**
  * Quickly check the current PHP version.
  */
-if (version_compare(PHP_VERSION, '5.4.0') < 0) {
-    exit('PHP 5.4+ is required (currently running PHP ' . PHP_VERSION . ')');
+if (version_compare(PHP_VERSION, '5.6.0') < 0) {
+    exit('PHP 5.6+ is required (currently running PHP ' . PHP_VERSION . ')');
 }
 
 /**

public/setup.php

@@ -12,8 +12,8 @@
 /**
  * Quickly check the current PHP version.
  */
-if (version_compare(PHP_VERSION, '5.4.0') < 0) {
-    exit('PHP 5.4+ is required (currently running PHP ' . PHP_VERSION . ')');
+if (version_compare(PHP_VERSION, '5.6.0') < 0) {
+    exit('PHP 5.6+ is required (currently running PHP ' . PHP_VERSION . ')');
 }
 
 /**