Create Async methods for calls to eway servers

[ChannelSix]

Are there any plans to implement async methods for calls to the eway servers? I had a quick look at the source, and RapidService.GetWebResponse seems like a good candidate.

[rollsch]

There is a netstandard branch of this library available that has this done. You should merge their changes in. They have also updated automapper and newtonsoft.json

https://github.com/visualeyes/eway-rapid-netstandard