Escape < and > properly in Tips. Losslessly compressed PNGs.

### Escape &lt; and &gt; properly in Tips.

There was an issue with &lt; and &gt;, because of which some arguments where not visible in tips.
The tips were misleading and confusing.

### Losslessly compressed PNGs, saved 62Kb

It is always good to compress images on the web.

### Remove unrelated tips

its_a_small_world.html had some tips from other step.