Add a line to .htaccess

This line is already active on the server
Move and shrink API section on about page

Reason: Most people visiting the Stacks project will not know what an API
is. IMHO it is more important for these people to go visit the
acknowledgements page and perhaps the github repositories for the
Stacks project. Moreover, somebody who is looking for an API will find it
because web search engines will give the location.

In fact I am a bit worried that the acknowledgements aren't sufficiently
visible but that is for another day.
Made a couple of changes to api.php

NOTE: I did not test these changes and in particular I did not visually
insspect the changes (same with previous commit).

If you somehow get to the API page, then you first see "Overview" but
you have no idea what this is an overview off. So I changed it to
 "API Overview".

I tried to improve the language a bit too but I am not sure I succeeded.
Anyway, otherwise it looks fine.