Add hint about getting already minified CSS and JS files.

Grunt use can be avoided for people only interested in changing the content
of the site.
Don't use the word "sponsors" for the wx-related ads.

First of all, this is not really correct as these are not paid ads at all.
Second, anything with "sponsors" in it is in the default AdBlock filter.
Shorten "Online Manual" in the quick links.

It is not necessary to mention "3.0" here.
Assume that everybody knows what "Hello World" is.

It seems redundant to say "Hello World Example".

Also point it to the latest example in the trunk, this page doesn't risk
becoming incompatible but can be improved.
Add wiki and roadmap back to the quick links.

The wiki link is important and should be emphasized. The roadmap link is not
easily accessible otherwise and its absence had been remarked upon by several
people in the past, before it was added, so there doesn't seem to be any
reason for removing it.