Native subsystem startup code

[daurnimator]

lib/std/start.zig should gain code for windows native subsystem programs.

From https://web.archive.org/web/20091207075651/http://technet.microsoft.com/en-us/sysinternals/bb897447.aspx:

Instead of winmain or main, the entry point for native applications is NtProcessStartup. Also unlike the other Win32 entry points, native applications must reach into a data structure passed as its sole parameter to locate command-line arguments.

The majority of a native application's runtime environment is provided by NTDLL.DLL, NT's native API export library. Native applications must create their own heap from which to allocate storage by using RtlCreateHeap, a NTDLL function. Memory is allocated from a heap with RtlAllocateHeap and freed with RtlFreeHeap. If a native application wishes to print something to the screen it must use the function NtDisplayString, which will output to the initialization Blue Screen.

Native applications don't simply return from their startup function like Win32 programs, since there is no runtime code to return to. Instead, they must terminate themselves by calling NtProcessTerminate.

Related to #1840