Improved server mode

[yhatt]

Current server mode is bit difficult to use because it requires to access file URL manually. This PR will provide served file list as the directory index. By accessing http://localhost:8080/, marp-cli shows the list of served markdown files.

Screenshot

Currently CLI provides the super-simple file list by using serve-index, but we can improve by our Pug template and SCSS.

I'm going to add a checkbox whether to toggle showing served static files (non-markdown files) in another PR.

?pdf query parameter

The improved server mode no longer recognize the conversion type option like --pdf. We always serve the deck as HTML by default.

Instead, we recognize ?pdf query parameter in accessed URL. You can execute the on-demand PDF conversion while serving HTML. The added directory index has the "PDF" link to trigger it.

http://localhost:8080/index.md?pdf

Default file (index.md or PITCHME.md)

As like as several web server, we recognize index.md as the default page of directory index. It means that you can see the slide deck by accessing http://localhost:8080/ if index.md is placed into the served directory.

If you are familiar to GitPitch, you can also place PITCHME.md to the directory.

ToDo

• Fix test about server mode

[yhatt]

UPDATE: By updating style, more beautiful file list of directory index is ready to use.