Improve fee market document and unify terminology

[hackfisher]

V3:
{
    confirm_relayer 落在哪个Slot Index, Slot price is the relayer ask for Slot Index.

    Message surplus = Message Fee - Slot price.

    1. 
      A: Slot Offensive Slash: ?For each assigned relayer's slot index < Slot index(Confirm), slash: a) collateral_const * 20% and no reward or b) slash function(t) in expriy time (> last slot)

    Message Reward = Slot price + Slot Offensive Slash

      B. Slot Duty Reward = Message surplus * 20% -> assigned relayers which >= Slot index(Confirm)  (If no relayers match the condition, Ask reward is zero)

    Message surplus -= Slot Duty Reward

    2. Message Reward -> (delivery_relayer, confirm_relayer)

    3. Treasury: Message surplus
}

[hackfisher]