Extend compress function

[Alejandro Tejada]

I just noticed that Mark Waddingham
wrote in 2011:

http://quality.runrev.com/show_bug.cgi?id=9553

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[snip]
Of course, this does suggest several potential improvements...
Add 'command' forms of compress and base64decode which
work very much like convert.

Perhaps a general 'decode' / 'encode' command for
encoding / decoding filters:

  decode tVar using ( base64 | ascii85 | ... )
  encode tVar using base64

And a compress / decompress pair for that sort of operation:
  compress tVar using ( deflate | bzip2 | gzip | ... )

These would then allow greater control over parameters to the filters.
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If you find these additions useful for your current or future
development work in this platform, please add your own
comments to this request:

http://quality.runrev.com/show_bug.cgi?id=10594

Thanks in advance!

Al