Help comment is unexpectedly mangled

[Timmmm]

I wrote the following code. I think it's a reasonable thing to do:

struct Opts {
    /// the target to build. One of:
    ///
    /// * clean                 Clean everything (including node_modules)
    /// * client                Build the Typescript extension client
    /// * isa                   Build the ISA processing tool
    /// * isa_generate          Use the ISA processing tool to generate the Rust code
    /// * npm_install           Run NPM install
    /// * package               Generate the VSIX package
    /// * release               Clean and rebuild everything and make a package
    /// * server                Build the Rust language server
    /// * tree_sitter_generate  Generate the Tree-Sitter C code from the grammar
    #[argh(positional)]
    target: Target,

Unfortunately it gets rendered in --help like this:

Positional Arguments:
  target            the target to build. One of: * clean                 Clean
                    everything (including node_modules) * client               
                    Build the Typescript extension client * isa                 
                     Build the ISA processing tool * isa_generate          Use
                    the ISA processing tool to generate the Rust code *
                    npm_install           Run NPM install * package             
                     Generate the VSIX package * release               Clean and
                    rebuild everything and make a package * server              
                     Build the Rust language server * tree_sitter_generate 
                    Generate the Tree-Sitter C code from the grammar

It seems like argh strips each line and then joins them into one string. I think that's a bit unexpected. Probably worth checking what structopt does.