Update the crate to use the latest version of the IGDB API

[Hukadan]

Hi,
I have updated this crate to use the latest version of the IGDB API. The main modifications are:

• a client_id and a token are now needed to use the API
• the surf crate seems to be unmaintained so I replaced it by the reqwest crate
• the examples can be run by setting environment variables instead of modifying examples themselves
• I have updated the dependencies (the async-std needs the tokio1 feature for the examples to run).

I have started to learn Rust not so long ago, so it might not be perfect.

Tests passes and examples work.

Thank you.

[Hukadan]

Hi,
Did you have time to look at my PR? If you are not interested in this crate anymore, do no hesitate to tell me and I will fork it instead.
Thank you for your time (and your code, from which I learned a lot).
Have a nice day.