title: Adding to a bit array
body: <p>In my program, I am using BitArrays to represent 160 bit numbers. I want to be able to add, subtract, increment and decrement these numbers, what is the algorithm for doing this?</p>
  
  <p>At the moment I'm not interested in multiplication and division, but I might be in the future so bonus points for that.</p>
  
  <p>I'm implementing in C#, but pseudocode is fine if you're not familiar with the language</p>