Add comments to enums/structs/funcs etc.

[eliasdaler]

Apparently, cimgui added comment support not that long ago, see cimgui/cimgui#212.
This is great, because we can add comments to struct getters, enum values and so on.

I'm adding this issue to track progress. For example, see this file as an example of what can be generated:
https://github.com/eliasdaler/cimgui-go/blob/enum_comments/cimgui_enums.go

Thoughts? :)

[AllenDang]

That will be great!

[gucio321]

well, despite I didn't tag this, that isseue is already fixed in #136