Build system is broken on macos

```
./configure --prefix=/something
make
make install
```

on darwin, I'm ending up (a) without pkg config files and (b) with an incorrect symlink:


```
$ ls -l lib/
librhash.1.dylib
librhash.so.1 -> librhash.1.dylib
```

Shouldn't it be `librhash.dylib -> librhash.1.dylib`?

I completely agree with #65, cause it's a major pain to build such a trivial package...