Vim syntax file for ZX BASIC

[programandala.net]

I've improved and updated the Vim syntax file for ZX BASIC. The block comments are not highlighted, I still don't understand why. Beside, I've tried to highlight Z80 code inside ASM zones, following the Vim documentation. It works partially: the ASM END is not recognized, I don't know why. Anyway, without block comments and Z80, the current version is better than the 2010 version.