First 14 distinct kernal instructions semi-implemented.

Status register is not yet being used, BEQ & BNE branch instructions
always branch.
Status register implemented.
12 more instruction types. Runs for 682,705 instructions.

Eventually crashes on unhandled instruction: TYA.
Instructions: BCS, CLC, DEY, TYA. Runs for 682,731 instructions.

panic: unhandled instruction: BPL
Instruction has id (int) not name (string).

This should provide faster dispatching to instruction methods.
An unscientific comparison showed ~20 sec runtime reduced by 2 sec.
BPL instruction. Now executes 682,945 instructions before crashing.

Eventual crash after 22 seconds:

--- Step 682945
R Bus[0xFD27] OffsetMemory(ROM[8k:rom/kernal.rom:8556..48ff]) --> 0x91
R Bus[0xFD28] OffsetMemory(ROM[8k:rom/kernal.rom:8556..48ff]) --> 0xC3
Instruction[STA op:91 addr:9 bytes:2 cycles:6] op8:0xC3 op16:0x0000
R Bus[0x00C3] (RAM 64K) --> 0x30
R Bus[0x00C4] (RAM 64K) --> 0xFD
W Bus[0xFD30] <-- 0x31

panic: ROM[8k:rom/kernal.rom:8556..48ff] is read-only

goroutine 1 [running]:
c64.(*Rom).Write(0x2101f7210, 0x311d30)
  /Users/pda/code/c64.go/src/c64/rom.go:33 +0xc0
c64.OffsetMemory.Write(0xe000, 0x2101f74e0, 0x2101f7210, 0x31fd30)
  /Users/pda/code/c64.go/src/c64/memory.go:30 +0x49
c64.(*OffsetMemory).Write(0x2102957a0, 0x31fd30)
  /Users/pda/code/c64.go/src/c64/bus.go:0 +0x9b
c64.(*Bus).Write(0x2101db1b0, 0x21031fd30)
  /Users/pda/code/c64.go/src/c64/bus.go:41 +0x1d6
c64.(*Cpu).STA(0x2101db220, 0x210221290)
  /Users/pda/code/c64.go/src/c64/cpu.go:377 +0x56
c64.(*Cpu).Execute(0x2101db220, 0x210221290)
  /Users/pda/code/c64.go/src/c64/cpu.go:211 +0x3df
c64.(*Cpu).Step(0x2101db220)
  /Users/pda/code/c64.go/src/c64/cpu.go:69 +0xf0
main.main()
  /Users/pda/code/c64.go/main.go:21 +0x278