Platform support

[Lendvai Attila]

Hi!

Some kind of a Platform object is missing more and more... I have some
vague ideas how it could be added, but this letter is more of a
discussion starter, then a specification of any kind.

lobby Platform were an instance of WindowsPlatform, UnixPlatform,
LinuxPlatform, etc

At image startup the global slot were initialized to the current
platform.

Stuff a Platform object is responsible for:
- isLittleEndian or Platform endianness (which returns a LittleEndian
and BigEndian object to dispatch on)
- guide the compiler about calling conventions, etc (later)
- answer various Platform specific backend implementations, like ui Port
impls, WindowsConsole

Issues:
- How should the VM set the platform slot at startup, Platform protos
must be added to bootstrap. (This is Lee territory... :)
- If once there are optimized platform endian WordArrays, Int16Arrays,
etc then these must be converted if the image is started up with a VM
with different endianness. This is not a live issue for now...

feel free to extend the lists, bring up ideas...

- 101