Fixes for link shares

[nielsranosch]

When creating a link share ('shareType' => 3), 'shareWith' is optional (in fact, the parameter will be ignored if given).

Additionally, 'expireDate' is not only available when updating a share, but also when creating one. The server processes and stores it correctly.

Tested on NextCloud 14.0.1

[ovesco]

Alright for the shareWith parameter but I didnt find any mention of expireDate for creating share in the API docs
https://docs.nextcloud.com/server/14/developer_manual/core/ocs-share-api.html

[nielsranosch]

True, I was suprised to find that as well. But after testing it, it seems they forget about it somehow.

By the way, there are a lot of compatibility issues with NextCloud 14, causing me to not use the plugin after all.

[kler]

There are a lot of functions in the API not Documented by Nextcloud :/
Unfortunately it's necessary to check their code instead.

I've implemented support for handling Nextcloud versions in the library, and also started implementing Nextcloud 14 and 15 compatibility in PR #3.