Contribution Guidelines and PHPCS Composer Removal

- Made changes to contribution guidelines to include instructions on how
  to use PHPCS.
- Removed PHPCS as a Composer development requirement.

CONTRIBUTING.md

@@ -4,12 +4,12 @@
 
 We use the [PSR2](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md) standard.
 
-[PHP CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer) is included as a Composer development requirement in order to help developers achieve PSR-2 compliance in any contributed code. 
+[PHP CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer) can be used to help developers achieve PSR-2 compliance in any contributed code. 
 
 ### Running PHP CodeSniffer
 
-- Install PHP CodeSniffer by running composer with development requirements (`composer install --dev`).
-- Execute `vendor/bin/phpcs --standard=psr2 src/Petrinet/*` from the project root directory
+- Install [PHP CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer#installation).
+- Execute `phpcs --standard=psr2 src/Petrinet/*` from the project root directory.
 
 ## Unit tests
 

composer.json

@@ -17,8 +17,7 @@
         "symfony/event-dispatcher": "~2.0"
     },
     "require-dev": {
-        "satooshi/php-coveralls": "dev-master",
-        "squizlabs/php_codesniffer": "1.*"
+        "satooshi/php-coveralls": "dev-master"
     },
     "autoload": {
         "psr-0": {