talkatu/talkatu

Migrate to gi-docgen and remove the doc comments that were gtk-doc specific

Testing Done:
Build the docs locally and via the convey plan.

Reviewed at https://reviews.imfreedom.org/r/1056/
# h1
## h2
### h3
#### h4
##### h5
###### h6
plain *emphasis* _emphasis_ ~~**strong**~~ __strong__ `code` plain
[Test link](https://pidgin.im)
`code`
```
code?
```