Automatically register NLog.Web LayoutRenders for NetCoreApp1

[snakefoot]

No longer need to add this for NetCoreApp1:

  <!-- Load the ASP.NET Core plugin -->
  <extensions>
    <add assembly="NLog.Web.AspNetCore"/>
  </extensions>

Guess the wiki-page has to be updated.

[codecov]

Codecov Report

Merging #249 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #249   +/-   ##
=====================================
  Coverage      59%    59%           
=====================================
  Files          29     29           
  Lines         395    395           
  Branches       92     92           
=====================================
  Hits          233    233           
  Misses        126    126           
  Partials       36     36

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[304NotModified]

Nice!