Extract CLI crate and add shell completion and man page

[mrgalopes]

Closes #27.

Adapted from the main typst repo. It only outputs the completions and the man page when the cli feature is enabled. A downside is that it always fetches and compiles the dependencies. Any suggestions are appreciated. 😄

[laurmaedje]

I think having clap as a build dependency unconditionally is unfortunate. If we want to do this, maybe the CLI should be extracted into its own crate like in Typst.

cc: @reknih

[LaurenzV]

Yeah, I actually also extracted it when I did the rewrite initially, but I didn't know whether that was what you wanted so I ended up reverting to using a cli feature. I also think having them separate would be nicer.

[laurmaedje]

Originally, I liked this setup, but I've come to prefer the more flexible two-crate setup since.

[mrgalopes]

Yeah, extracting the CLI into its own crate should be nicer, you're right. I will update the PR in the following days with this setup. Thank you for the feedback!

[mrgalopes]

I separated the crates inspired by the structure of typst, and also rebased on main. Let me know what you think.

[mrgalopes]

Apologies for the delay. I've been looking for alternatives to add the completions but couldn't find any that were ideal. The way that this was done mirrors the typst-cli, where the nix flake installs the completion after the build. Without nix, this would have to be done manually. From what I could find, crates.io doesn't let you install arbitrary files, like completion files. This is how I've done for zsh:

1. Update the .zshrc to include a folder that looks for completions and to autoload them

   
   fpath+=~/.zfunc

autoload -Uz compinit compinit

2. Copy the completion artifact corresponding to zsh and bash to the ~/.zfunc folder, and restart the shell
```sh
cp target/release/artifacts/_svg2pdf ~/.zfunc

[laurmaedje]

Thank you!