Markdown support for duplicate section names

[seebees]

In markdown you can create duplicate header names.
Each header is an anchor,
but the duplicates get a number.

# Foo
This is the first foo section

# Foo
This is the second foo section

# Bar

Now if I want to link [first foo](#foo),
but if I want to link [second foo](#foo-1).

Here is a more complicated example:

https://github.com/awslabs/aws-encryption-sdk-specification/blob/master/framework/structures.md

The extract succeeds,
but it only creates TOML files
for one section.

It appears to stomp on the file,
and so the result is the last section seen.

[seebees]

Also, doing the extract manually,
the report does not succeed.

Updating the created TOML file
for the above example to plaintext-data-key-1.toml
and editing it target = "aws-encryption-sdk-specification/framework/structures.md#plaintext-data-key-1"
The report still returns section "plaintext-data-key-1" not found in "aws-encryption-sdk-specification/framework/structures.md"