* ICalculator.cs: added overflow detection

* NumericInputBuffer.cs: added back the sanity max length check

* TraditionalCalculator.cs: reworkd the sign function, so that it's
  entirely an aspect of the inputBuffer state
made it so that all inputs result in the buffer bineg pulled into the
  CalculatorEngine

* NumericDisplay.cs: added the capability of display scientific
  notation

* TestCalculatorEngine.cs: added additonal test cases

* TestTraditionalCalculator.cs: added additional test cases

* CalculatorEngine.cs: slightly improved implementation
fixed one bug where the operator was not being properly overwritten
  added overflow detection
added appache license
readme file