added Decimal type example for C#
corrected errors about the nullable types for C#
mentioned strings immutability and added details about var keyword (C#)
typo (not instead of note) for C# doc
corrections for C# doc
added details for the switch statement for C#
more details for the enums (C#)
various typos + added an example to declare an auto property (C#)
added an example for the foreach loop in C#
breaking some lines (C#)
added myself to the contributors (C#)
Merge pull request #364 from yaurthek/csharp_improvements

[csharp/en] C# improvements