The C# client does not have asynchronous versions of cache operations

The current implementation allows for asynchronous invocation of all methods through C# Task API in this way:

await Task.Run(() => cache.Put(k,v)).

However, it is common in C# to have asynchronous methods ending with "Async" (e.g. StreamReader has ReadLineAsync link StreamReader.ReadLineAsync)

The goal is to simplify programming with these methods and allow the caller to call just:

await cache.PutAsync(k,v)

The .NET client should provide asynchronous versions of basic operations such as put, get, etc. All the operations of the original Java client should have their "async" equivalents:

• GetAsync
• PutAsync
• PutIfAbsent
• PutAllAsync
• ClearAsync
• RemoveAsync
• ReplaceAsync
• ReplaceWithVersionAsync
• RemoveWithVersionAsync