Feat: add bearer authorization

[kilianmh]

• Add bearer authorization option to all request methods
• Break keyword parameter lines so they do not exceed 100 chars
• Expand authorization section in readme

Nowadays a lot of API use Bearer instead of Basic Authorization.

I was not sure how to best implement tests for the request headers. I tested on Linux X86 and on Windows and bearer-auth works for me on both.

[fukamachi]

I don't want to add keywords for each authorization scheme (e.g., digest-auth, hoga-auth, etc.), but I think it's fine to add one only for Bearer since it's the most popular.

[fukamachi]

Thanks!