Filesystem stuff on Windows

Minor image acquire/present refactor
Unsigned integer limits
Fixed typo in arena push/push copy macro

code/os/impl/windows/core.c

@@ -1,3 +1,19 @@
+// Windows utilities
+
+internal Str8 Win32_WideStr(M_Arena *arena, Str8 v) {
+	Str8 result = { 0 };
+
+	S32 nchars = MultiByteToWideChar(CP_UTF8, 0, (LPCCH) v.data, (int) v.count, 0, 0) + 1;
+	U64 nbytes = nchars << 1;
+
+	result.count = nbytes - 2; // -2 because we don't include the null-terminator in the count
+	result.data  = M_ArenaPush(arena, U8, .count = nbytes);
+
+	MultiByteToWideChar(CP_UTF8, 0, (LPCCH) v.data, (int) v.count, (LPWSTR) result.data, nchars);
+
+	return result;
+}
+
 // Virtual memory
 
 U64 VM_PageSize() {
@@ -36,3 +52,4 @@ void VM_Release(void *base, U64 size) {
 	VirtualFree(base, 0, MEM_RELEASE);
 }
 
+#include "filesystem.c"