JK Flip-Flop

On rising edge of i_clk:

• J=0, K=0: hold (no change)
• J=0, K=1: reset (o_q <= '0')
• J=1, K=0: set (o_q <= '1')
• J=1, K=1: toggle (o_q <= not o_q)

Asynchronous reset forces output to '0'.