The type of the user being created is defined at creation time. This
allows the creation of basic users.
Although the users can be created internally, they cannot yet be created
via maxadmin or the REST API.
The Users class now performs locking when a method is called. This will
prevent concurrent access to the internal map of users.
Added missing const versions of SpinLockGuard.
Made the USERS an opaque object to reduce the amount of exposed
interfaces. Moved the storage of users into a C++ class and exposed that
class via the users interface functions.
Removed unused code and cleaned up the documentation in the header. Added
helper functions for printing the stored users.
