Export ParseError, import URL

[edemaine]

This should enable fixing

https://github.com/DanielXMoore/Civet/blob/6197b5a53e510a9519df437c8e86c2c8198118c7/types/types.d.ts#L58

by adding this to parser.hera:

```
export { ParseError }
```

Also, yarn test isn't working on Windows, with error Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only URLs with a scheme in: file, data, and node are supported by the default ESM loader. On Windows, absolute paths must be valid file:// URLs. Received protocol 'c:'. I added some code that should fix this, but still doesn't seem to. Progress though I think.

I also updated the ParseError interface and constructor to provide more convenience:

• header field for the main message (first line after filename:line:column)
• body field for the multiple lines of expected rules
• message isn't an argument, but is automatically constructed as filename:line:column header\nbody
• No more name argument; it should be "ParseError" in all cases

[edemaine]

Thanks! Could you release?