[SockoBot] Implementation of STEEM vote's value calculator

Task request

My implementation is referred to task request by Hive account@jestemkioskiem, the new SockoBot $vote command functionality.

Today's task request has to do with addition of new functionality to SockoBot - a $vote command that will calculate given user's vote's value and return it as a discord message.

Development

For last days I was learning how STEEM's upvote calculation works. In SockoBot we wanted to achieve the same upvote value estimation like we see under articles. By using Discord command we could estimate how valuable will be our upvote.

For that all we need is specific user's vests amount, his voting power and current blockchain reward/claims ratio. These all should be multiplied by SBD to dollars exchange rate. Last what I needed was get_current_median_history_price func from Steemit API.

As You can see the formula is a little complicated. I needed few hours to get to how it should be solved but after utopian.io bugfix #248 contribution I was sure how this is to be done.