Module splitting

[RustyNova016]

I started splitting the modules into multiples ones according to #25. For now only Core is made, but I am creating this pull request for tracking and initial review

Here's some details:

• I changed the response_type macro to have absolute paths and thus being able to be used in children modules.
• I changed the way the separation comments are made. Now it is {request type} {apipath}, like shown in the official documentation. While the original ones are closer to string formatting, the new ones are easier to find with a ctrl-f from the official documentation.
• I also added a link to the official documentation for quick referencing
• The types have been sorted by order of appearances in the user documentation.

[InputUsername]

Hi @RustyNova016, for the next release (0.8.1) I'd like to merge this PR first, but there are merge conflicts now. Would you be able to solve those? If not, feel free to close this PR and create a new one.

I really like these changes though, great job :+1: