DNS6, DOMAIN, and Cache changes

A number of pull-requests and updates added, fixing some bugs and adding new features. Thanks go to @piotr-dobrogost, @thecodingrobot, @tbaumann, @Edu4rdSHL, @adq, @bohlstry, and @dannyk81 for their assistance.

Add support for ADAPTER_DOMAIN_SUFFIX

Following a request by @JoshDobbin, support has been added for passing ADAPTER_DOMAIN_SUFFIX via dhcp-options to work with the Microsoft standard. Also included some additional notes in README.md about using down in dropped privilege situations for clarification.

Fix logger Issue and Documentation Corrections

Improvements made to the logger command to prevent issues with privilege dropping under the assistance of @dermarens, @terminalmage, @guruxu, and @benvh. Updated some documentation for consistency and clarity. Thanks to @flungo and @dawansv here.

Documentation Update

Thanks to @piotr-dobrogost, @mgu, and @aRkadeFR for helping to improve the documentation.

Documentation Update

Thanks to @piotr-dobrogost, @mgu, and @aRkadeFR for helping to improve the documentation.

Makefile Improvements

@Nauxuron provided a patch to improve DESTDIR and PREFIX handling in Makefile.

OpenVPN 2.4 Fixes & DNSSEC Improvements

This one is with thanks to @mikken and helps support OpenVPN 2.4 as well as fix an issue with DNSSEC handling on the busctl call.

IPv6 DNS Fix

Thanks for @arjenschol for spotting this one: An error in the AF_INET value provided to SetLinkDNS prevented IPv6 DNS servers from being added.

A Few Improvements

Add support for DNSSEC processing, improve logic around DOMAIN and DOMAIN-SEARCH handling, add support for DOMAIN-ROUTE, and improve documentation.

Documentation Updates

Thanks to the help from @pid1 for this release. The documentation mistakenly noted to use pre-down for the script now (compared to down originally, which failed as the tun or tap device would have been removed before the script ran). However, this should have in fact been down-pre.