Rename classes matching .NET classes

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There are few classes with the same name as .NET has:

• CodeJam.HashCode - System.HashCode
• CodeJam.Collections.CollectionExtensions - System.Collections.Generic.CollectionExtensions
• CodeJam.Ranges.Range - System.Range

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@igor-tkachev @andrewvk What do you think?
I know it is a breaking change but it makes writing code a little bit harder.
Or we just leave it as it ?

[rameel]

CollectionExtensions does not conflict with System.Collections.Generic.CollectionExtensions, and is rarely used directly by name, except perhaps when creating a delegate (method group). Therefore, I don't see a reason to change its name.

HashCode, we can rename it to HashHelper or HashUtil as an example.
Range - I have no thoughts.