New project files.

I made new project files so the libraries can be added as target dependencies and linked in, and so that the headers can be included from the build products directory.

This makes the project a bit more similar to how a normal Xcode library would behave, although rebuilding the libraries still requires manual input. The build scripts will skip building if the library is already built, so if you change the version you have to clean the targets. Cleaning from within Xcode works fine, no need to go delete the derived data from the finder.

Building libssh2 requires automake, autoconf and GNU libtool but since even the original scripts added brew / macports to the path I don't think that's a big issue.