pad issues with leading zeros so issues sort properly

[nbsmith]

Is your feature request related to a problem? Please describe.
The default behavior is to download with the issue number as is from the site. It's frustrating as the comic reader I use gets the order of the issues confused when going from issue to issue. issue-10 often
comes after issue-1 rather than issue-2 being next.

Describe the solution you'd like
A flag that takes in a zero padding number or by default has a padding of at least 3. So issues by default, go issue-001, issue 002.

Describe alternatives you've considered
A folder rename program or batch file. Sub-optimal as it adds an extra step.

Additional context
I have already implemented this for myself in the form of defaulting 3 digit padding. It also takes into account that some sites have 1.1, 1.2, 1.5, etc. Resulting in 001.1, 001.2, 001.5.

Tested with several comics with no issues aside from when a comic has a mix of regular issue-1, issue-2, and then issue-2.5. Resulting in issue-001, issue-002, and issue-002.5 which some readers will be confused and open issue-002.5 first before issue-002.

I have not figured out a good solution for the last part other than manually renaming issue-002 to issue-002.0. I don't think users will like a solution that does decimal by default.