Compress text output files

[wtraylor]

The text output files can build up to substantial size. It would be convenient to have the option that they are automatically compressed when the simulation is complete.

• Add TOML key output.text_tables.compression with the options "none" and "gzip".
• If "gzip" is selected, each TSV output file gets compressed at the end of the simulation or on the fly. That creates for instance mass_density_per_hft.tsv.gz.
• The demo_results.Rmd file checks if the output is compressed, and if so, uses R’s gzfile() function to decompress it on the fly. Compare this stackoverflow post.
• As for a library, a wrapper around zlib seems to be the way to go. There are gzstream and zstr, which both expose C++11 output streams.