Created Missing Number project

This is a C# console application that reads a file line-by-line and finds the missing value in each line. The results are written to a second file. 

I added a little bit of reusability and flexibility to the project by creating a file processor class whose ProcessFile function accepts a delegate that can be changed to process the lines of text in different ways, say, with a function that would put each line in alphabetical order. Further flexibility *could* be added by allowing different output methods, say, Console.WriteLine(), but I left it for now.. 

Also, the MissingNumberFinder is allowed to concern itself only with finding missing numbers. Should the definition of a missing number change (or we decided to allow for more than one missing number in a single line), that would be the only class that needs to change.

Normally, these kinds of classes would be in a separate library assembly and in a separate namespace, but I kept the files all together in the name of simplicity.