Initialization sequence

On boot, we jump to the "main" routine in boot.fs which does
very few things.

1. Set SP to 0x10000-6
2. Sets HERE to RAMEND (RAMSTART+0x80).
3. Sets CURRENT to value of LATEST field in stable ABI.
4. Look for the word "BOOT" and calls it.

In a normal system, BOOT is in icore and does a few things:

1. Find "(c<)" a set CINPTR to it (what C< calls).
2. Initialize all overrides to 0.
3. Write LATEST in BOOT C< PTR ( see below )
4. Find "INIT". If found, execute. Otherwise, "INTERPRET"(cont)