Added manpage

[k-lar]

I added a manpage like I said I would in my previous pull request.

The manpage is generated with pandoc through converting a markdown file to the correct format. At first I wanted to commit just the markdown file to the repository and make the users compile the manpage, but that would mean that they would need to have pandoc installed. I think it's a better idea to have both files in the repo so that we get out of the way of users when they just want to download the tool and install it as fast as possible and with no added dependencies.

The Makefile has been updated with a manpage target, to streamline the generation process. The install and uninstall targets have also been updated to include the installation and deletion of the included manpage.

I've also added a mini version changer script to make it easier to keep versions in multiple files consistent.

[paldepind]

Thank you! The PR looks great. I definitely think that it's a great idea to include both the generated man page and the Markdown file, such that Pandoc is not a built dependency.

I think it would be nice to move version_changer.sh into the docs/ directory. Maybe the name does not imply that, but it is the intention that it should contain miscellaneous files for documentation and maintenance.

[k-lar]

I put it in the docs folder now, I also made it more robust and defined paths, so that you can run the script from anywhere and it will still make the changes to the correct files.

[paldepind]

Looks good! 👍 Thanks again for the PR.