Create NLog.Extensions.Logging v1.7.5 using NLog 4.7.15

[snakefoot]

Based from https://github.com/NLog/NLog.Extensions.Logging/tree/v1.7.4

With dependency-update: https://www.nuget.org/packages/NLog/4.7.15 (Update from NLog v4.7.11)

[304NotModified]

@snakefoot do you think this is still needed?

[snakefoot]

@304NotModified Yes I would like a release that includes the fix of the critical bug included with NLog v4.7.12

If you create a branch, then I don't mind doing the pull-request (maybe want to make some extra fixes)

[snakefoot]

Created new branch with the fixes:

https://github.com/NLog/NLog.Extensions.Logging/tree/v1.7/

What should be done to get a proper build released?

[snakefoot]

Believe I figured out how to turn the branch into an official release:

https://www.nuget.org/packages/NLog.Extensions.Logging/1.7.5