This commit adds support for Epson scanners. It packages the iscan
application, the epkowa SANE backend, iscan-data, as well as the
scanner-specific plugin for the GT S650 (and by extension V19 and V39).
More scanner plugins may be added later when people request them.
iscan is unfree because it ships with a binary blob. sane-epkowa is
free, however, same as iscan-data. Scanner plugins are unfree again.
All unfree components are covered by the AVASYS license. Not only does
it allow distribution, it's also almost a free license. However, it
forbids reverse engineering the binary blobs.
The binary blobs make this x86/amd64-only packages. The epkowa backend
itself could technically be compiled for other architectures, but it's
not evident that it's worth the time. Most modern scanners need a
proprietary plugin.
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