[avr-libc-dev] Clean documentation: remove __ATTR_CONST__

[Dmitry K.]

Hi.

Now the file doxygen.config.in (CVS head) is changed.
The Doxygen's CPP will evaluate macroses (which are listen)
and substitute an empty string instead __ATTR_CONST__
(see ChangeLog).

I check this with Doxygen 1.4.7: OK, the __ATTR_CONST__
label is removed.

Is there any objections to this?
If no objections, I will remove all other __ATTR_-es.

Dmitry.