Issue72 Deprecate Add<T> method in favor of Set<T>

[matthew-p]

An attempt to address issue # 72, deprecating the IAppCache.Add(...) method with a .Set() method

Replaces the functionality as-is, adds [Obsolete] attributes to the Add method, and a unit test to confirm that all classes implementing IAppCache have an Obsolete attribute on their Add method

#72

[alastairtree]

This looks great, thank you. Will leave this here until i have setup a branch for the 3.0 changes. Thanks!

[jnyrup]

Tip:
To prevent IntelliSense from suggestion both Set and Add you can add [EditorBrowsable(EditorBrowsableState.Never)] to the obsolete methods.

[alastairtree]

Tip:
To prevent IntelliSense from suggestion both Set and Add you can add [EditorBrowsable(EditorBrowsableState.Never)] to the obsolete methods.

Did not know that, very useful! Let's use it.