Convert to PSR-2 code style

Used [Code
Sniffer](http://pear.php.net/package/PHP_CodeSniffer/redirected) and
[PHP-CS-Fixer](https://github.com/fabpot/PHP-CS-Fixer) to do guide the
fixes to Mongodm.

Most fixes are related to spacing issues:

- tabs to spaces
- 4 spaces rather than 2
- space after function declaration
- etc...

There are some occasions where I changed private methods to protected to
better support issues related to prefixed _

There should be further refactoring to standardize method names to camel
case as most of the code is in camel case while deprecating malformed
methods. However this may be a further conversation due to issues
related to "appearing" like the PHP Mongo methods which use
non-camel-case.