[barcode] Patch for table printing

[Markus Berg]

Hello Allesandro,

first off: thank you for this wonderful software. We use it at the
office for printing labels for our backup tapes. However, I've been
having some problems with table printing. The 'barcode' frontend doesn't
give me enough control over where on the page the barcodes are printed,
and their size.

So I wrote a patch (see attachment).

Changes:
* This patch differentiates between barcode padding and barcode margins.
The width and height parameters of the "-g" switch sets the full width
and height of the barcodes including padding.

* The "-m" switch only affects inner-table margins

* If barcode width and height are not specified, the table expands to
fill the page (minus page margins), and the barcodes themselves expand
to fill up the table (minus inner-table "-m" margins and barcode
padding).

* Automatic page break if the table is too large to fit on one page

Please let me know what you think.
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best regards
Markus Berg