Support OnProgress in Push / PushOptions

Feature Request:

When pushing to a remote repository its currently possible to handle callbacks for OnPushStatusError OnPushTransferProgress and OnPackBuilderProgress but there is currently no way to handle the OnProgress callback similar to the one that is available for Fetch (through FetchOptions).

This feature request comes out of this question posted on StackOverflow:
http://stackoverflow.com/questions/22149891/remote-response-when-pushing-with-libgit2sharp

I've been looking through the code to get an idea of how this should be implemented, and I'll post back with a pull request and/or additional questions once I get into it.

Bắt đầu bằng cách so sánh các entry point Push và PushOptions với FetchOptions, sau đó theo dõi các callback OnPushStatusError, OnPushTransferProgress và OnPackBuilderProgress hiện có. Được xem là hoàn thành khi các caller có thể xử lý callback OnProgress trong khi push theo cách nhìn chung giống như khi fetch.