Also, is_admin and can_create_group are exposed in the user information.
Fixed attributes_for_keys to process properly keys with boolean values (since false.present? is false).

The API docs incorrectly referenced a few attributes associated with users. The 'blocked' attribute has been replaced with 'state'. Also, 'dark_scheme' seems to no longer be available in the User model so it should be removed from the exposed attributes in the API User entity.

Add color scheme ID to API User entity

Most of these are comments but a few are strings for users.

Might be an idea to run this from time to time:
https://github.com/lyda/misspell-check

It runs mostly clean now.

All the info to return codes from the API functions are available in the `README.md` file as suggested.

The users API updated with return codes, e.g. if required parameters are missing
a `400 Bad Request` error is returned instead of `404`. Fixes return codes of functions,
e.g. deletion of a ssh key is an idempotent function now.
The API documentation is updated to reflect the current status of the API. Descriptions
are more detailed and complete, infos to return values are added to all functions.

Information to return codes added to projects and users documentation.

Also added tests.

The 2 reasons are :
- creation of user fail if name is empty : in after_save, it tries to create a
namespace with namespace.name = user.name and namespece validates presence
Namespace#name
- in the web app links to team members are broken with empty User#name because
they are of the form <a href'...'> user.name </a>