standard build using GNU autotools

With this PR sickle can now be built, tested and deployed using standard GNU autotools.

Run `./bootstrap` to generate `configure` and others and then the following will install sickle into `/usr/bin/sickle`:

```
./configure --prefix=/usr
make
make install
```

I have also added two tests to what I could make of the files you had in the `test` directory.

You can still create a standard release tarball using `make dist`.

If you have questions about GNU autotools, just let me know. The required autoconf version could maybe be lowered in `configure.ac`, try testing it if you have an older one.