Snapshot, build, and PC-98

• MS-DOS image building now uses git submodule reference to necessary libraries.
• Cleanup and improve IBM PC/XT/AT BIOS snapshot tools
• Added NEC PC-9801/9821 BIOS snapshot tools, which uses the same code as IBM PC/XT/AT targets but contains code specific to A20 gate control on PC-98 rather than IBM PC platforms.

General release

doslib2-20171227

more

doslib2-20140703-220240-commit-06b4977782d6beb8f4b5929843cb23dfa3147846

Binary output and OBJ, LIB files of commit doslib2-20140703-220240-commit-06b4977782d6beb8f4b5929843cb23dfa3147846