Add alternative autotools build system

As usual with autotools:
```
./autogen.sh
./configure
make
make install
```
It builds everything, including the Python module.

It does not install the examples and the documentation.

If someone could review and/or test this, it would be great. No doubt there are some stupid things to point out.

I believe it builds imwri successfully (if ImageMagick is compiled with the right options). CC those affected by issue #116 .