Made xkcd_desc an f string, added spoiler `||` on either side so when it's posted to discord it spoilers the text.

Attempting to create a command that takes in a course code, selected year, semester, mode, and campus and then provides the link to the course profile.

Currently it defaults to the current semester and I'm yet to work out how to make it not default.

Need to format the embedded and allow it to take in multiple courses

It assume when requesting you want the same semester, year, mode and campus for all courses.

- Fixed typo
- Clarified error message
- Changes wording of the else statement that in theory should never happen because of the exceptions.

Unsure if this will cause issues, doesn't look like it and improve any future use of checking what the estimated current semester is.