Include a quick demo screen recording.

Forgot to return here to exit when more than one file is dragged onto
the drop zone.

The application only has one window, and it doesn't really work if that
window is closed.

Also remove the unused `applicationDidFinishLaunching:` delegate method.

Just in case. Was getting a runtime exception occasionally and am still
not entirely sure why. It happened in the `[Server stop]` call.

Also check if the process is running before terminating it. Didn't read
about whether we're required to do this, but it seemed logical.

Previously, when the file path of the folder being served was long, it
would resize the window to fit the path.

Prevent resizing, and truncate the path label so that it truncates the
beginning of the path and keeps the end.

Thanks to Stephan (https://stackoverflow.com/users/565336/stephan) on
Stack Overflow for the tip about setting

> Content Compression Resistance Priority of the NSTextView less than
> NSLayoutPriorityWindowSizeStayPut (e.g. 499). Otherwise your
> NSTextView will not truncate its content.

(https://stackoverflow.com/questions/4171465/truncate-nstextview/13977990#13977990)

Use consistent indentation. Looks like I've been using tabs here, so
change everything to tabs. Some code was generated at the start of the
project, or I copied it from Apple reference documents, or it was
inserted from an Xcode snippet.

Noticed that sometimes the server wasn't stopped when it should have
been. Thought maybe I should use `terminate` instead of `interrupt` to
be sure that the process exits.

There's a noticeable delay with one second.

Saw during testing that the browser could try to load the page before
the server had started up.