Check if a valid username.
    valid:
        oracle
        bill-gates
        steve.jobs
        micro_soft
    not valid
        Bill Gates - no space allowed
        me@yo.com - @ is not a valid character
    :param username: string
    :return:

def is_username_valid(username):
    """
    Check if a valid username.
    valid:
        oracle
        bill-gates
        steve.jobs
        micro_soft
    not valid
        Bill Gates - no space allowed
        me@yo.com - @ is not a valid character
    :param username: string
    :return:
    """
    pattern = re.compile(r"^[a-zA-Z0-9_.-]+$")
    return bool(pattern.match(username))