Markdown file does not get generated when a reference is used

## What did you do

I have two simple schemas: `foo` and `bar`. `foo` references `bar` via a property called `bar`. There is a `$ref` in the declaration of that property.

## What did you expect to happen

The links in all generated documents should be valid.

## What happened

When the markdown files are generated, the `foo.md` file contains a link to `foo-properties-bar.md` which doesn't exist.

## Do you have example files:

I am attaching a zip with the schema files and the generated markdown files.

[test.zip](https://github.com/adobe/jsonschema2md/files/5357366/test.zip)

Unpack the attached test.zip and inspect the schema files and generated foo.md. Start by tracing how the property reference to bar is turned into the foo-properties-bar.md link. Done means the referenced Markdown document is generated or the link is corrected so all links in the generated documents are valid.

Written by the indexing model from the issue text.