Build process clean up

I want to remove the spec file, clean up the Makefile a bit and also fix a bug where the manual pages are getting the wrong version number.

The argument for getting rid of the spec file is that it is old, out of date and incompatible with the way archives are built.
The argument against it is that this will encourage people to reinvent the wheel by writing their own spec files. I already provide some at http://github.com/zanchey/fish-build/.

This will probably break the Xcode build and I can't work out how to edit it manually, so if someone could work out how to pass `FISH_BUILD_VERSION` to `build_tools/build_documentation.sh` that would be good.