Feature/hard link

[Daniel-KM]

To hard link files is quicker, safe, and space efficient. So this pull request add an option to enable it.

This pr is based on previous ones, but i can separate it if needed.

[Daniel-KM]

Rebased.

[jimsafley]

I don't fully know what problem this is solving, but it seems to have a narrow use case, so I'm unconvinced of it's value to our general audience. Given the amount of code this introduces, we have to weigh the feature's value with the amount of work it will take to maintain into the long term.

[Daniel-KM]

This is for people who have a small hard drive. It increases performance too, since temp is done on the same hard drive than other files. But this is not so frequent nowadays.

[jimsafley]

Thanks for the clarification. I'm going to let this one sit until we have a sense that it has broader appeal from our users. To my knowledge, no one has expressed need for this, and I hesitate to merge a feature (especially one that requires a specific configuration on the server) without gauging our users' needs.