Support AppendBlobs and AppendBlock operation

[joaocc]

Hi, These seem to be supported on API version 2015-02-21 and later.

• https://docs.microsoft.com/en-us/rest/api/storageservices/understanding-block-blobs--append-blobs--and-page-blobs#about-append-blobs
• https://docs.microsoft.com/en-us/rest/api/storageservices/append-block

It would be great if this new method could be added. Thx

[deadlyfingers]

With .NET 4.6 (Experiment) support looming I have held fire on developing this as it looks like we are close to being able to use the full SDKs now in Unity. https://docs.microsoft.com/en-us/sandbox/gamedev/unity/azure-storage-unity

[joaocc]

Thx. Didn't knew about that. We will try it, but the fact that it doesn't work on HTTPS is not good for us at the time being (Hololens/UPW on a non-game scenario). Anyway, we will prob try to add Append to your code and submit a PR.