Included new fields

We've added 'watchlist_portfolio_users' field to /coins/{id} endpoint responses.

This refers to number of users who added the coin into a watchlist or portfolio.

Example of responses:

{
"id": "bitcoin",
......
"watchlist_portfolio_users": 1449601, 👈
"market_cap_rank": 1,
......
"tickers": []
}