Fetch links default behaviour

[Vitalium]

In my project I need to always fetch all links. I reviewed source code and noticed that fetch_link is set to False in kwargs everywhere. Of course, I can subclass Document and change signatures of all functions by changing fetch_link to True. But maybe it will be useful to set default action (True or False) somewhere is global settings/options?

[roman-right]

Sounds good. Yup, I'll add this to my todo