Consider dropping alternate compression methods

[Peter Hyman]

After the discussion on zstd #61 support, it dawned on me there will always be some new "better" compressor or one that becomes fashionable.

gzip is gzip, bzip is bzip, zpaq is zpaq, lzo is lzo, even lzma is lzma. lrzip files using those compression methods are incompatible with the native applications. Since lzma has been shown to be overall better than all the others -- either in terms of time and compression ratio, what benefit is there to keeping alternatives? rzip+lzma is all that is needed.

As you mentioned, @ckolivas , no one is using the library.

One program, one purpose.

I suggest we prune down the codebase and dump all the alternative compression methods and the library. Pure lrzip will be the result.

JM2C