Add words to write to interrupt vectors

[tkers]

There currently is no (nice) way to write interrupt handlers.

Workarounds for now would be to:

• Manually write bytes in the $0000 - $00ff range using c!
• Get the ROM offset with here and force emit code after setting the offset with ==>

A possible improvement would be to implements words like :interrupt1 (or the equivalent for code) that emit the definition/asm to the correct address.