Update Kerbanomics.cs

Added calculations for compound interest rates to the file...
Update Kerbanomics.cs

Fixed comments (duh).  put in the Math.pow() function instead of ^ notation.

I really need to get a compiler working on this box to check this.

Added a big comment block on how to structure the calculations more like a real-life loan.
Merge pull request #1 from divisionbyzero1/patch-1

Update Kerbanomics.cs for proper APR calculations.