Gut install.html

[Paolo Carlini]

Jonathan Wakely wrote:

>I don't think it hurts to have that info in two places, but I'll look at
>merging the texts and making the FAQ just point to install.html to
>answer the question once.
>  
>
Thanks. If you could also work a bit on finding a better home for:

    http://gcc.gnu.org/onlinedocs/libstdc++/ext/howto.html#5

as already briefly discussed some time ago...

Thanks in advance,
Paolo.