Intent to Implement: additional OpenX amp-ad optional parameters

This is only for OpenX amp-ads. attributes to add:

data-inventory-type (naming subject to change) A number of our partners just want to reuse their old inventories instead of making a new set for AMP. With the inventory type, they will not be stuck to mobile inventories and will be able to use regular desktop ones. If this is missing, OpenX will refer to the partner's mobile inventory.
data-lower-limit (naming subject to change) An optional attribute that would let a partner only accept a bid of this limit or higher, else, pass as a default to doubleclick. If not defined in the tag, the lower limit is 0.

ampproject / amphtml