ref #162 make dependencies runtime rather than compile time

specifically CGI::File::Temp and HTML::Entities - this offsets the
approx 0.03s extra it takes to compile the module due to the removal
of the AUTOLOAD functionality[1]:

	current master:
	> time perl -MCGI -e1
	real    0m0.040s

	AUTOLOAD removed:
	> time perl -Ilib -MCGI -e1
	real    0m0.070s

	AUTOLOAD removed and this change:
	> time perl -Ilib -MCGI -e1
	real    0m0.039s

some users are rather vocal about a compile time difference of +0.05s[2]
so this change aims to appease them. frankly if +0.05s on compile time
makes that big a difference to you then perhaps you should re-evaluate
using CGI in a none-persistent environment?

[1] profiling with Devel::NYTProf shows the same timings, and more
interestingly shows that (as expected) *every single* subroutine call
made to or in the CGI package goes through AUTOLOAD and _compile, and
that has overhead - looking at Devel::NYTProf we can optimise the
_make_tag_func out into something that is built at compile time and
not have the function built everytime the tag function is called.
this cleans up the code significantly

[2] https://github.com/leejo/CGI.pm/issues/162#issuecomment-67541469