Support CoinGecko Pro API

[n8maninger]

The currently supported endpoint only works with a demo API key or without an API key. A couple changes are necessary to use the CoinGecko Pro API:

• https://api.coingecko.com -> https://pro-api.coingecko.com
• x-cg-demo-api-key -> x-cg-pro-api-key

Documentation can be found here: https://docs.coingecko.com/reference/authentication

Might be best to have two CoinGecko sources. If no key is available, use the free API, otherwise use the pro API.

[chris124567]

I think you always need to provide an API key now, because I've tried a blank API key or just omitting the header altogether and they return errors.

https://www.reddit.com/r/coingecko/comments/1amkl77/public_keyless_api_deprecation/