Add ToArray method and tests

[jreina]

https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.toarray?view=netcore-2.1

[roopbiswas]

I would like to work on this. Can you please elaborate what the issue requires?

[jreina]

The issue requires the creation of a new method, ToArray following the existing convention for methods in the project (new file at ./ShittyLINQ/ToArray.cs), as well as the addition of a set of tests for the new methods. Again, the tests should follow the same convention as existing tests and should verify correctness when used properly, and also that the proper exception is thrown when used improperly (i.e. source is null). The newly added method should have the type signature and behavior described in the specification here