Add maxOccurs and minOccurs logic for nested elements

[LeonidKrutovsky]

<xs:sequence>
    <xs:element name="Color" type="tt:ColorOptions" minOccurs="0">
        ...
    </xs:element>
    <xs:element name="Transparent" type="tt:IntRange" minOccurs="0">
        ...
    </xs:element>
    <xs:element name="Extension" type="tt:OSDColorOptionsExtension" minOccurs="0"/>
</xs:sequence>

minOccurs = 0 => Optional; minOccurs > 1 || maxOccurs > 1 => Vec; maxOccurs = 1 || minOccurs = 1 => Type;