1) In `README.md`, we shouldn't use `c#` but `csharp` to make md
recoginize it's the C# formation of codes.
2) Add 'ConfigureAwait(false)' as for the MSDN magazine usage.
3) Don't need Contribution History in README.md, because we can see the
change logs in GitHub instead.
1) Considering using xUnit for UnitTest, remove my unit tests.
2) Remove useless `async`, because `async` is just the wrapper of `Task`.
3) Modify unit tests to be sure that the values MUST BE equal to each other when the IP is the same.
