Replace fraction stuffs with Perquintil

[readlnh]

darwinia/srml/staking/src/lib.rs

Line 1556 in 368a8d3

let reward = Perbill::from_rational_approximation(p, points.total) * total_payout;

Since total_payout may be larger than 10,000,000,000, should we consider replace Perbill with Perquintil?

[readlnh]

8c72b06
Now the error rate is only 100.

[aurexav]

close via #183