[BUG] Grouping multiples files rendering issue

```
index.apib
# Group A

---

child-A.apib
# Child A [/path]
## Some API [POST]
## Another API [GET]

---

child-B.apib
# Child B [/path]
## Some Other API [POST]

---->

This results in the sidebar looking like this
Group A (expandable)
- Child A
- Some API
- Another API
- Some Other API

---

but it should look like this
Group A (expandable)
- Child A
- Some API
- Another API
- Child B
- Some Other API

---

or even ideally like this
Group A (expandable)
- Group Child A (expandable)
- Some API
- Another API
- Group Child B (expandable)
- Some Other API
```

Now if you add another method to child-B it renders the way it should be

Changing it to this format somewhat fixes the issue
```
index.apib
# Group A

---

child-A.apib
# Child A [/path]
## Some API [POST]
## Another API [GET]

---

child-B.apib
# Child B [GET /path]

---->

however this format you have to have all single method children files at the top of the group otherwise they fall into other child sections
```