add another ruby gem

[2pd]

This is another ruby gem to use BTCMarkets Public API

• V3 support
• private methods, including placing order, cancel order, etc
• test cases included.

[martin-nginio]

Hi @2pd

Thanks for your support and adding the Ruby version for API v3.

I will merge this file and will also add link to your project to our official API v3 documentation .

Thanks.

Regards, Martin