Added Server.php hooks for creating and updating CouchDB users

[synatree]

I needed to be able to create and update users on CouchDB in PHP7. Respectfully submitted.

[lornajane]

I would LOVE to have this feature, thanks so much for the pull request! There are a couple of small things that are required though, hopefully you are still keen enough to make some changes (and if not that is fine too but please let me know in case anyone else wants to pick this up):

• first, the build failed on coding standards. I'm sorry this project should have a CONTRIBUTING file and I will add that, but for now the info you need is here https://github.com/ibm-watson-data-lab/php-couchdb#for-developers on how to run the tests and the codesniffer check
• the @author tag isn't usually included at a per-method level (people will see your contribution through GitHub itself)
• this feature needs a test. Take a look at the tests directory and let me know if you need more information than "please write a test". I'm happy to help but don't want to be patronising!

[lornajane]

Just a quick ping to check if you're OK to pick up the comments above? If not, no worries.

[synatree]

Sure, I'll loop around and revisit this in a few days.

[synatree]

I have not yet written any tests... but at least the spacing and formatting issues are resolved. BTW, the build passed phpcs the first time, but not --standard=PSR-2