documentation update + code fixes

docs/contributing/clean-code.md

@@ -0,0 +1,60 @@
+Clean Code
+==========
+
+We have added some development tools for you to contribute to the library with clean code: 
+
+- **PHP mess detector**: Takes a given PHP source code base and look for several potential problems within that source.
+- **PHP code sniffer**: Tokenizes PHP, Javascript and CSS files and detectes violations of a defined set of coding 
+    standards.
+- **PHP code fixer**: Analyzes some PHP source code and tries to fix coding standards issues. 
+- **Tests**: Well, everybody knows why tests exists. 
+
+Using PHP mess detector
+-----------------------
+
+PHP mess detector takes a given PHP source code base and look for several potential problems within that source. The 
+following is a sample usage with all options available: 
+
+```bash
+./vendor/bin/phpmd ./src text codesize,unusedcode,naming,design,controversial,cleancode
+```
+
+For further information, please visit [PHP mess detector documentation](https://phpmd.org/)
+
+Using PHP code sniffer 
+----------------------
+
+Global settings file: `phpcs.xml.dist` (added into Git)  
+Local settings file (you can add it locally): `phpcs.xml` (ignored by Git)
+
+- Run checking by `PHP_CodeSniffer`: `./vendor/bin/phpcs`  
+- Show check report in patch form: `./vendor/bin/phpcs --report=diff`  
+- Automatically fix all fixable issues: `./vendor/bin/phpcbf`
+
+For further information, please visit [squizlabs/PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer)
+
+Using PHP code fixer 
+--------------------
+
+Global settings file: `.php_cs.dist` (added into Git)  
+Local settings file (you can add it locally): `.php_cs` (ignored by Git)
+
+- Run checking by `PHP-CS-Fixer`: `./vendor/bin/php-cs-fixer --config=.php_cs.dist fix ./src  --dry-run`  
+- Automatically fix all fixable issues: ` ./vendor/bin/php-cs-fixer --config=.php_cs.dist fix ./src`
+
+For further information, please visit [FriendsOfPHP/PHP-CS-Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer)
+
+Running Tests
+-------------
+
+We are using `Codeception` for testing the module. Do the following: 
+
+- Create a `yii2-usuario-test` database. 
+- Add database access configuration `tests/_app/config/db.php` 
+- Run `./vendor/bin/codecept build`
+- Run `./vendor/bin/codecept functional`
+
+We still need to add `unit` tests to the module. Feel free to add your tests to it as long as it makes use of 
+`Codeception`. 
+
+© [2amigos](http://www.2amigos.us/) 2013-2017