Added additional error checking to ReadNumberOfTestCases

- added constants for maximum and minimum allowed test cases
- renamed Solution.ReadNumberOfPoints to Solution.ReadNumberOfTestCases
- changed Solution.Main to return when numberOfTestCases < 0 since these can be
  used as error codes
- Solution.ReadNumberOfTestCases now checks to see if the number entered is in
  the range determined by MinimumNumberOfTestCases and MaximumNumberOfTestCases
  inclusively and returns -2 if the number is not in range
Renamed global variable names