Handling of &nbsp and other html entries in gfm

According to the [specification](https://github.github.com/gfm/#entity-references) gfm supports html entries like ` `. Are they supported by this library? If so, how?

Given a test case:
```
Hello World! Docs with period issue, e.g. this.
```

using:
```
val gfmFlavourDescriptor = GFMFlavourDescriptor()
val markdownAstRoot = IntellijMarkdownParser(gfmFlavourDescriptor).buildMarkdownTreeFromString(testString)
```

I get a text node from 37 to 52 instead of some code or other form of marker that this fragment contains html entry.