Improve the installation process & some minor changes

[SqrtMinusOne]

A bunch of changes to resolve the problems I had with installing this package. Hope you don't mind some refactoring.

First, there's a convention that the prefix of the package has to be the same as the package name, i.e. dank-mode- in this case (maybe in the future someone makes a package called dank-posts that does something totally different). So I changed the names accordingly. You'll most likely be required to do so anyhow if you submit this to MELPA.

This also allows for having one main file dank-mode.el, which lists all the dependencies of the package. Which I've also done, so now the package can be installed with straight.el, sans this issue. I added a paragraph with a workaround to the README.

Also:

• Enabled lexical binding everywhere. MELPA also requires this.
• Added a note that the OAuth dance won't work in EXWM
• Added a variable dank-mode-prefer-new-reddit to prefer reddit.com over old.reddit.com
• Changed dank-mode-comments-browse-post-link, dank-mode-comments-browse-post-comments, dank-mode-posts-browse-post-link-at-point and dank-mode-posts-browse-post-comments-at-point to set the eww argument with the prefix argument. Otherwise the argument is always nil.

[john2x]

Thank you for this. I wasn't aware about the naming requirement for submitting to MELPA, and I do intend to submit this one in the future.

[john2x]

LGTM