--version should report latest (current) version of SLAX supported

`slaxproc --version` gives lots of information, but not the _current_ version of libslax:

```
% slaxproc --version
libslax version 0.22.2-git-develop
Using libxml 20909, libxslt 10133 and libexslt 820
slaxproc was compiled against libxml 20909, libxslt 10133 and libexslt 820
libxslt 10133 was compiled against libxml 20909
libexslt 820 was compiled against libxml 20909
```