Add optional bsdcat tool

Tool acts like zcat/bzcat/xzcat/<whatever>cat, but uses libarchive to auto-detect compression format - i.e. `bsdcat file1.txt.gz file2.txt.bz2 file3.txt.xz > all_files.txt` should just work.

I coped this thing from an libarchive code example as a simple ["excat" tool](http://sourceforge.net/projects/excat/) a while ago, but recently Markus (he didn't provide full name) sent me the patch integrating the tool into libarchive (and including manpage), asking to forward it upstream with rationale that it'd be a handy tool to have on systems with libarchive out of the box.

Code is more complex than original 10-liner excat, as I've updated it to fit with libarchive style a bit more and parse commandline arguments properly with getopt.
Tool builds and works, but I don't usually write C code outside of small patches and minor glue, and don't deal with autotools aside from packaging and build fixes, so have to suggest to not auto-merge this pull request without at least looking over the changes.

Would it be useful to merge it into libarchive alongside bsdtar/bsdcpio?

Thanks.