Create createAccount

bool createAccount (string $pUsername, string $pPassword, $pEmail) 
    Attempt to create an account for the passed in  
    username,  password, and email.
    
    Requirements: A mysql database containing a table called "users".
    
    
    Performs the following checks:
    
    1) Checks if a valid email has been provided
    2) Checks if email already exists.
    3) Checks that username is between 4 and 15 characters
    4) Checks that password is longer than 6 characters
    5) Checks if username already exists
    
    If ALL checks pass, it performs the following tasks:
    
    1) Creates user account to table users, where password is inserted after being hashed
    2) Emails the new user a link to activate his/her account