Change type of compression field of variable structure
Change type of compression field of variable structure

* src/matio.h (struct matvar_t): Change type of compression field to
      enum matio_compression

CBL-ORION/matio-sf-mirror,martinichka/matio-coder,CBL-ORION/matio-sf-mirror,tbeu/matio,martinichka/matio-coder,tbeu/matio,MaartenBent/matio,telehan/libmatio,MaartenBent/matio,martinichka/matio-coder,tbeu/matio,MaartenBent/matio,CBL-ORION/matio,CBL-ORION/matio,tbeu/matio,NJannasch/matio,MaartenBent/matio,telehan/libmatio,NJannasch/matio