Fix arithmetic operators and code examples

Indentation and spacing causing some code examples to render incorrectly on the main site (although not on GH). Also corrected multiplication operator in the arithmetic operators table, and added the VB integer division operator as the equivalent for Python's floor division operator.

I was tempted to alter usage of MsgBox to Debug.Print (which is closer to Python's print statement/function) but I suspect most VB users don't know about the global Debug object and just put up with MsgBox and endless clicking on Ok...
Merge pull request #3 from waveform80/patch-1

Fix arithmetic operators and code examples