Support OpenSSL 1.1.1

[L-as]

This PR updates to version 0.10 of the OpenSSL crate to support version 1.1.1 of OpenSSL.
To do this, I had to update some other crates across breaking changes, however serenity still compiles and all tests pass, but I can not assert that everything works alright.
In addition, I do not know if any of the changed crates are public dependencies, because if so, this is a breaking change too.

[Erk-]

We have used our own branch because of a bug happening with the websocket crate. For more information about that read the #394 issue. This is already fixed on the next major version where it will also be possible to use rustls for tls.

[L-as]

Sounds great! Where can I find the next major version?

[arqunis]

The next major version is v.0.6.x, albeit the rustls support hasn't been merged yet, but it will.

[Erk-]

If you use v.0.6.x I would recommend setting a commit you use as there is still major changes there are waiting to be merged. For example:

[dependencies.serenity]
git = "https://github.com/serenity-rs/serenity"
rev = "3c166e3"

[L-as]

Thanks! I will close this PR now since it's obviously unneeded.