Add autoconf/automake scripts

[jonsneyers]

Because standard ./configure; make; make install is nice, and it will make life much easier for distro package maintainers.

[rtzui]

Please don't. Installing the proper version of libpng and sdl is way easier than installing the proper version of autotools.

And the makefile now is probably more portable aswell.

[c0nk]

There is no point in having autoconf/automake scripts. There are already CMake files, which are more portable than autoconf. Nowadays, CMake is just as standard as ./configure + make and distro package maintainers shouldn't have any issue building with CMake.