Fix bug in 'opendcp_decoder_openexr.c' and add float functions for 'opendcp_image'

[SieuDoTia]

Fix bug in opendcp_decoder_openexr.c and add float functions for opendcp_image.h and opendcp_image.c. Float functions use float image data (range 0.0 to 1.0) replace integer data (0 to 4095) for high dynamic range image. Only opendcp_decoder_openexr.c use it because only OpenEXR have high dynamic range data. If want use integer data for opendcp_decoder_openexr.c change lines: line 854: opendcp_image_t *image = opendcp_image_create(3, image_data.width, image_data.height); line 861-863: image->component[0].data[index] = (int)image_data.channel_b[index]*4095.0; image->component[1].data[index] = (int)image_data.channel_g[index]*4095.0; image->component[2].data[index] = (int)image_data.channel_r[index]*4095.0;

If find bug please tell me.