code: function (cpu, mmu, cc) {
      if (cc) {
          cpu.pc += 2 + mmu.readByte(cpu.pc + 1).signed();
          return 12;
      }
      cpu.pc += 2;
  
      return 8;
  }
docs: JR cc,n
  
  Description:
  If following condition is true then add n address and jump to it:
  
  Use with:
  n = one byte signed immediate value
  cc = NZ, Jump if Z flag is reset.
  cc = Z, Jump if Z flag is set.
  cc = NC, Jump if C flag is reset.
  cc = C, Jump if C flag is set.
  
  Opcodes:
  Instruction    Parameters    Opcode    Cycles
  JR             NZ,*          20        8
  JR             Z,*           28        8
  JR             NC,*          30        8
  JR             C,*           38        8