fix project names with nested dirs

[mbpowers]

when inputting a name in the cli that contains /, nested directories are created

fixes #98

[JohnBakhmat]

I would also consider adding "/" check then. So that some like me doesn't override his root directory with melange app

[dmmulroy]

Rather than this fix, and supporting nested directories, I would like to prohibit nested directories. Lets instead update this function in https://github.com/dmmulroy/create-melange-app/blob/develop/src/core/fs.ml to return a result and fail if there are invalid characters or slashes in the name here:

let parse_project_name_and_dir (str : string) =
  let trimmed = trim_trailing_slash str in
  if String.equal trimmed "." then
    let name = [| trimmed |] |> Nodejs.Path.resolve |> Nodejs.Path.basename in
    let directory = [| Nodejs.Process.cwd () |] |> Nodejs.Path.resolve in
    (name, directory)
  else
    let name = [| trimmed |] |> Nodejs.Path.resolve |> Nodejs.Path.basename in
    let directory =
      [| trimmed; name |] |> Nodejs.Path.resolve |> Nodejs.Path.dirname
    in
    (name, directory)
;;

[mbpowers]

okay I think this should be good