Refactor file writing - introduce template driven file writing

apps/CA.pl and tools/c_rehash are built from template files.  So far,
this was done by Configure, which created its own problems as it
forced everyone to reconfigure just because one of the template files
had changed.
Instead, have those files created as part of the normal build in apps/
and in tools/.

Furthermore, this prepares for a future where Configure may produce
entirely other build files than Makefile, and the latter can't be
guaranteed to be the holder of all information for other scripts.
Instead, configdata.pm (described below) becomes the center of
configuration information.

This introduces a few new things:

%config         a hash table to hold all kinds of configuration data
                that can be used by any other script.
configdata.pm   a perl module that Configure writes.  It currently
                holds the hash tables %config and %target.
util/dofile.pl  a script that takes a template on STDIN and outputs
                the result after applying configuration data on it.
                It's supposed to be called like this:

                        perl -I$(TOP) -Mconfigdata < template > result

                or

                        perl -I$(TOP) -Mconfigdata templ1 templ2 ... > result

                Note: util/dofile.pl requires Text::Template.

As part of this changed, remove a number of variables that are really
just copies of entries in %target, and use %target directly.  The
exceptions are $target{cflags} and $target{lflags}, they do get copied
to $cflags and $lflags.  The reason for this is that those variable
potentially go through a lot of changes and would rather deserve a
place in %config.  That, however, is for another commit.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>