Deep inheritance analyzis

Fixing default attribute values remove check for deep inheritance.
And removing useless overrides with the same value as inherited, for example:

    <svg xmlns="http://www.w3.org/2000/svg">
        <g fill="red">
            <g fill="red">
                <g fill="green">
                    <g fill="green">
                        <path fill="red" d="M18.8 86.9l39.2"/>        
                    </g>
                </g>
                <path fill="red" d="M118.8 186.9l79.2"/>
            </g>
        </g>
    </svg>

->

    <svg xmlns="http://www.w3.org/2000/svg">
        <g fill="red">
            <g>
                <g fill="green">
                    <g>
                        <path fill="red" d="M18.8 86.9l39.2"/>
                    </g>
                </g>
                <path d="M118.8 186.9l79.2"/>
            </g>
        </g>
    </svg>