New features

#165 - It's now possible to specify your own CSR (and optional private key) to the program to create a Let's Encrypt certificate with specific settings that are unavailable otherwise. This is implemented as a new target plugin, that's usable both from the command line and interactively. See the documentation.
#940 - It's now possible to specify the --reuse-privatekey parameter at creation time to re-use the same private key across renewals. A stable private key makes it easier to publish long-lived TLSA records.
The program will now create a daily log file of its operations in {ConfigurationPath}\Log going back one month. The path can be customized using the setting <LogPath>. Further logging configuration is as always handled by Serilog and may be modified through wacs.exe.config with AppSettings, but this is not supported and for advanced users only.

Enhancements

#1128 - DNS pre-validation should be much more reliable now. Like regular DNS resolvers, it now uses a top-down algorithm instead of a bottom-up one to find authoritative name servers. It also recognizes NS records provided as part of a SOA statements now, which it previously failed to do. Furthermore using the DnsServer override in settings.config no longer stops us from looking for authoritative name servers; it merely overrides the starting point.
#1175 - It's now possible to execute multiple installation scripts by editing the .json file. This not supported by the command line or the interactive interface yet though. Based on an experiment by @Virinum.
#1144, #1171 and others - By popular request, the PemFiles plugin will now also output a -crt.pem file with just the certificate (before it was only available as part of the -chain.pem file).
Only count successful history entries for the "n renewals" label in the certificate details.
In Advanced Interactive Mode, if the only remaining installation option is "Do not add extra installation steps", simply skip the question.
Error handling has been improved to stop Autofac's DependencyResolutionException to barf over the screen so often, making it easier to see where in the programs code it actually went wrong.
Installation script output is now shown on-screen in --verbose mode, previously it only was logged to the Event Viewer, which was confusing.

#1176 - The client didn't support the "processing" status for authorization challenges. While not used by Let's Encrypt and BuyPass, it could cause issues for other ACME servers. Thanks for the PR @Geogboe.