use less -r instead of less -R for -p option

[namespaceYcZ]

According to less's manual page, -R option cause only ANSI "color" escape sequences output in raw form.

mdcat -p uses -R, which makes emojis and links look ugly in less:
(sorry for wiping out my privicy from the pictures)
(first picture: my test.md content)

(second picture: mdcat test.md, perfect)

(third picture: mdcat test.md -p (default to less -R, exactly the same as mdcat test.md|less -R)

(fourth picture: mdcat test.md|less -r, much better)

[swsnr]

Would you make a merge request to fix this?

[swsnr]

Never mind, fixed it.

[swsnr]

Fixed by a7d8ce3