New platform proposal: DOS

[nicholatian]

Slick already supports the IBMPC platform moniker for targeting old x86 computers. This is a proposal to create a distinct platform moniker called DOS, as it is actually quite a different deal to target than just any IBM-PC.

In the interest of completing #16, the IBMPC platform will run in huge unreal mode, potentially on bare metal, targeting the i386 as if it were running big-britches on a protected mode OS (that means 32-bit code and data pointers). IBMPC binaries will be compiled using a normal i386-producing ELF-bearing GCC, similar to APE. By contrast, the DOS platform will run in protected mode, using DPMI system calls provided by the DJGPP compiler toolchain.

TL;DR: the machines are the same, and the binary interfaces have the same characteristics, but the reality of how each platform is constructed and executed is very different. Whether IBMPC or DOS is more appropriate depends on the application.