Relocatable bytecode

[bobbimanners]

At present bytecode uses absolute addresses for branches / jumps and is not relocatable. It may be better to use relative branches / jumps so code can be readily relocated within VM memory.
Advantages:

• Portability of bytecode from Linux to Apple II, VIC20, C64 etc.
• Portability of bytecode between the 8 bit platforms.
• Eventually, allows some sort of module loading system (a bit like PLASMA has).

Drawbacks:

• Makes debugging bytecode more painful - this can be overcome with better tools though.

To implement this, we need to add new VM instructions and modify the compiler to use them.

[bobbimanners]

At present, for code to be compatible, both RTPCSTART and RTCALLSTACKTOP must have the same values (in eightballvm.h).