Filesystem stuff on Windows

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

code/os/filesystem.h

@@ -0,0 +1,16 @@
+#if !defined(LD_OS_FILESYSTEM_H_)
+#define LD_OS_FILESYSTEM_H_
+
+typedef U32 FS_AccessFlags;
+enum {
+	FS_ACCESS_READ  = (1 << 0),
+	FS_ACCESS_WRITE = (1 << 1)
+};
+
+function OS_Handle FS_FileOpen(Str8 path, FS_AccessFlags access);
+function void      FS_FileClose(OS_Handle file);
+
+function void FS_FileRead(OS_Handle file, void *ptr, U64 size, U64 offset);
+function void FS_FileWrite(OS_Handle file, void *ptr, U64 size, U64 offset);
+
+#endif  // LD_OS_FILESYSTEM_H_