Add --cxml flag

[lexh]

Closes #15

[jefftriplett]

This is great and saves me a ton of time! Thank you for opening the pull request.

[lexh]

FYI there is a degenerate behavior in this patch when no files are passed in.

> files-to-prompt --xml
</documents>

Not sure there is too much of an appetite for this to be merged in. Trying to read Simon's mind, the existing implementation probably gives comparable results while using less tokens and being more simple.

But I'll push another commit to better handle that case anyway.

[simonw]

Yeah let’s fix that and ship this!

[simonw]

I don’t like including this prompt here

[simonw]

The fact that this doesn’t guarantee a valid XML document (that could then be handled by an XML parser) really bugs me!

A few options:

1. Have it produce valid XML, which mainly means applying correct escaping to text between the XML tags. I’m worried this may hurt Claude’s performance, we would need to test that but I’m not sure how best to do that.
2. Admit that this isn’t valid XML and change the option to something like -c/--cxml (for Claude XML).
3. Call this XML but have another option, --valid-xml - which does produce valid XML and by its very existence calls out the Claude not-valid-XML thing.

I’m leaning towards 2.

[jefftriplett]

• Admit that this isn’t valid XML and change the option to something like -c/--cxml (for Claude XML).

This feels like a good compromise and opens the door for a valid --xml option later.

I have tested with both valid and Claude's XML, and I don't see any noticeable improvements either way. They have other features where randomly dropping in an xml tag has meaning in an otherwise other text sea of chaos.