Support bz2 compression for rdf input files to rdf2hdt CLI

[donpellegrino]

It would be a useful convenience if the rdf2hdt command-line interface (CLI) accepted bzip2 compressed triple files as input and handled the streaming decompression automatically.

[donpellegrino]

See also drobilla/serd#34

[D063520]

Note: this functionality is available in the hdt-java repo

[KonradHoeffner]

I think the most elegant way to solve this for all compression formats at once would be to accept standard input.
Then you could hook up whatever decompressor you want and pipe it into the rdf2hdt cli.