Add commandline flag to disable gzip compression

[mmokrejs]

User can only provide output file prefix, actually path followed by the prefix. One cannot affect whether the files created during --separate will be compressed or not. Luckily one can at leats for some work use the --stdout* flags but flag like --disable-compression would be handy.

Ideally the Makefile would allow to switch between gzip and bzip2, or allow both. Then, I would prefer:

--compression-method [supported values are gzip, bzip2, provided they were enabled during compile step]
--disable-compression [disable compression on all outputs, helpful when multiple files are created via --separate]