feat: Make voter electing staisfy finality

[kukugi]

Closes: #115

Description

Change voter election to satisfy finality.

changes

Sort voters in descending voting power/staking power.
Pick up a voter in order until total staking power of voters equal to total staking power of validators
If total voting power of voters picked up less than 1/3 of total voting power then stop electing

change and write test code to fit new election

---

For contributor use:

• Wrote tests
• Updated CHANGELOG_PENDING.md
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments
• Re-reviewed Files changed in the Github PR explorer

[egonspace]

You can sort this in-place. And the caller sortVoters(voters) has no effect with out-place sorting.

[kukugi]

ok i see, it can solve for changing caller sortVoters(voters) to voters = sortVoters(voters)

[egonspace]

When we first created the Sampling function, we implemented it in libs/land/sampling.go for general use, but now it doensn't need to be in the libs module anymore because it refers to a lot of voter-related contents such as 'voting power'. How about to move this implementation into voter_set.go and get rid of the Candidate interface?

[kukugi]

When we first created the Sampling function, we implemented it in libs/land/sampling.go for general use, but now it doensn't need to be in the libs module anymore because it refers to a lot of voter-related contents such as 'voting power'. How about to move this implementation into voter_set.go and get rid of the Candidate interface?

thanks for your review, I'll give it a try.

[egonspace]

When we first created the Sampling function, we implemented it in libs/land/sampling.go for general use, but now it doensn't need to be in the libs module anymore because it refers to a lot of voter-related contents such as 'voting power'. How about to move this implementation into voter_set.go and get rid of the Candidate interface?

thanks for your review, I'll give it a try.

Let's talk about this in next weekly.

[kukugi]

Create new PR without private branch to use Circle CI Large docker plan #124