NSFe regn section support

[vrubleg]

NSFe specification was updated to support additional useful features. I'd like to use the new regn section to specify that a specific NSFe file should be played in Dendy mode. You can use nsfplay as an example of program which already supports the new headers. You can use this NSFe file for testing. It has this new regn section, it states that it supports NTSC, PAL and Dendy timings, but marks Dendy as a preferred system.