Mark Adorable Avatars as HTTPS capable

While their main website returns the wrong certificate, the actual API does support HTTPS

Minor Housekeeping and Slack/eBay addition

I would certainly hope everyone looking through this list is looking for APIs, no need to hammer the extra word in everywhere.

This closes #159

Initially I have just taken the URL to the API - if it is https:// I
have assumed it does, if it doesn't I have assumed the opposite.

There may be some incorrect but as an initial update I thought that was
the safest way

Update README.md

Add Machine Learning APIs

Alphabetical order

This closes issue #256

Add BigOven to drink category

Add Uber API

Add Vagalume to Music category

Add Category Note for Contributing Guide

Add Edamam to drink category

Add Foursquare API info

Avoid service duplication in README (see: https://github.com/toddmotto/public-apis/pull/259#issuecomment-269635584).

Use https for OMDB

Fix MovieDB Auth

Fix Riot Games

https://developer.riotgames.com/docs/api-keys

Add Pearson dictionary API