Implement get market summaries call

[kirhgoff]

Currently there is no way to get all bid/asks for all markets at once (or is there?), I have to get quotes one by one and it is very slow. API documentation describe it here
https://bittrex.com/Home/Api (search /public/getmarketsummaries)

Any chance this could be implemented?

[arunsatyarth]

This is alredy present. Call Bittrex::Summary.all