In SANE 1, frontend has to list almost all options in order to build a
relation table of index -> option_name (or use a struct like xsane).
I suggest to use directly option name (SANE_String) as referer.
This imply also that, instead of a "option-count" option, we provide a
sane_device_list_options (handle) call which retourn a NULL terminated
array of SANE_Option_Descriptor. Then, this make sense to use Macro for
Well-Known option name.
As a summary :
* Define sane_device_list_options (handle) which return a NULL
terminated array of SANE_Option_Descriptor
* Use string instead of integer to refer options
* Define well know option macr (e.g. SANE_OPTION_RESOLUTION