CreateUser
CreateUser(UserId AS Integer, Name AS String [, FirstName AS String [, Level AS Integer]]) AS Integer
Creates a user with name <Name>, first name <FirstName> and access level <Level> then returns the ID of the created user in <UserId>.
If the user of name <Name> and first name <FirstName> already exists, his ID is directly returned in <UserId>.
<FirstName> and <Level> are optional (default: <FirstName> is empty, <Level> = 0).
Returns an error code (0 if no error).