Added a command line option to output a single hour

[Badboy-16]

I tried to fix #3

I added the -s (--single) option to the command line input and enabled the programme to output a single hour.

Usage:
Output a single hour for current time.

$ timezone-converter hong_kong tokyo -s now
$ timezone-converter hong_kong tokyo --single now

Output a given hour specified by the user (e.g. 16).

$ timezone-converter hong_kong tokyo -s 16
$ timezone-converter hong_kong tokyo --single 16

[Badboy-16]

Just pushed some commits based on your comments above. I think it's definitely a good idea to use a default value that can be changed later just like in #15 . Thanks for the reminder to utilise it again! 👍🏼

I tested the output with the single hour option and it looks working fine.

[ibLeDy]

pre-commit.ci run

[ibLeDy]

We will have to wait a bit for pre-commit to run, because seems like GitHub is having issues:

[ibLeDy]

pre-commit.ci run

[ibLeDy]

pre-commit.ci autofix

[ibLeDy]

This looks good, I will create a release in a bit, thanks!