documentation update + code fixes

docs/contributing/clean-code.md

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+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

docs/contributing/how-to.md

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+# How to contribute
+
+Contributions are **welcome** and will be fully **credited**.
+
+We accept contributions via Pull Requests on [Github](https://github.com/2amigos/yii2-usuario).
+
+
+## Pull Requests
+
+- **[PSR-2 Coding Standard](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md)** - The easiest way to apply the conventions is to install [PHP Code Sniffer](http://pear.php.net/package/PHP_CodeSniffer).
+
+- **Add tests!** - Your new features won't be accepted if it doesn't have tests.
+
+- **Document any change in behaviour** - Make sure the `README.md` and any other relevant documentation are kept up-to-date.
+
+- **Consider our release cycle** - We try to follow [SemVer v2.0.0](http://semver.org/). Randomly breaking public APIs is not an option.
+
+- **Create feature branches** - Don't ask us to pull from your master branch.
+
+- **One pull request per feature** - If you want to do more than one thing, send multiple pull requests.
+
+- **Send coherent history** - Make sure each individual commit in your pull request is meaningful. If you had to make multiple intermediate commits while developing, please squash them before submitting.
+
+
+## Clean Code
+
+- Follow the guidelines at [Clean Code](clean-code.md) 
+
+
+© [2amigos](http://www.2amigos.us/) 2013-2017