marketpress - payment gateway- ccavenue issue

I found the following extract in usage tab of market press
"Here are simple fully-documented plugin APIs for adding your own custom Shipping or Payment Gateway modules."
I however could not find any thing related to the things / coding that I should follow to make my own script for integration with ccavenue payment gateway.

I have been waiting for this payment gateway module in market press since last year. But I am yet to see any indication even for this gateway? Please help.