directory structure, header, license, favicon,..

I have reorganised the directories a little, placing CSS, JavaScript and
images into a new "assets" directory. I have also changed the "include"
directory to "includes", for some reason. There's only one include so it
can't be grammar.

The license has also changed, being changed from GPL v2 to GPL v3.
Keeping with the times, yo. The required files have been updated too.

I have added a good favicon too. I usually unclude 16-, 32-, 48-, 64-,
128- and 256-pixel square images in a single favicon, but I decided to
skip the 356-pixel one this round, as it little more than cumbersome.

Some other smaller things have changed. Files have been updated to
reflect the changes in directory layout and file names.

The JavaScript, for instance, has changed because I spaced out a few
blocks of code in it. Much more readable.