HTML report redesign & small report

I tried to adapt the look a bit like LCOV, so it's more readable for people that are used to using it. It also fixes the fact that rows looked huge in Firefox & IE. 

The biggest change is that I've removed the full border on each cell, and now it looks more like a source file view. I've also coloured the line number and count columns.

I have also created an additional option to print a small report which will only display the percentage to stdout.