make serve.cmd useful for everyone out of the box.

make serve.cmd useful for everyone and use sensible defaults, so it works for different editions out of the box.

Hi Jeremy, 
.\serve.cmd now supports a help question ... `serve help` now prints: 

```
Serve TiddlyWiki5 over HTTP

Optional parameters
 - %1 .. editions directory .. full path or relative to current directory
 - %2 .. username for signing edits - can be empty like this: '""'
 - %3 .. password - can be empty like this: '""'
 - %4 .. IP address or HOST name .. defaults to localhost
 - %5 .. PORT .. defaults to 8080

Example 1 .\serve .\edition\tw5.com-server username
Example 2 .\serve .\edition\tw5.com-server '""' '""' localhost 9090
.. Example 2 defines: empty username, empty password
```

So now I can say: `serve .\editions\de-AT-DE-server pmario` and it will start a dev server for the german editon.

If you just type `server` it will start your setting, so there are no changes for your workflow, but everyone else can use the script now, without the need to modify it. 

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I'd like to change the `serve.sh` file in a similar way but there will be a bit more `bash magic` to make it happen. 

"Usging" is a typo