bug: doctoc does not respect "id" attribute of headers when constructing the TOC

[flisboac]

When I try to generate TOC for a file that starts like such:

<!-- START doctoc -->
<!-- END doctoc -->

# Test 1

<h1 id="test-a">Test á</a>

I'd expect doctoc to generate a second TOC entry that respects the explicit "id":

<!-- START doctoc -->
- [Test 1](#test-1)
- [Test á](#test-a)
<!-- END doctoc -->

# Test 1

<h1 id="teste-a">Teste á</h1>

Instead, I get an autogenerated slug regardless:

<!-- START doctoc -->
- [Test 1](#test-1)
- [Test á](#test-%C3%A1)
<!-- END doctoc -->

# Test 1

<h1 id="teste-a">Teste á</h1>

Is that correct? If not, how difficult would it be for a fix to be made? I can help, if someone points me to the right places.

[AndrewSouthpaw]

Seems like a reasonable assumption to make, and sounds like it could be an improvement!

The codebase is pretty small, I think here would be a decent place to begin your investigation.