Build failure from master

[rickystewart]

Attempting to run mvn package yields many compile errors along the lines of the following:

[ERROR] /Users/ricky/go/src/github.com/JetBrains/teamcity-webhooks/webhooks-server/src/main/java/jetbrains/buildServer/webhook/WebhooksEventListener.java:[5,40] cannot find symbol
[ERROR]   symbol:   class IOGuard
[ERROR]   location: package jetbrains.buildServer.serverSide
[ERROR] /Users/ricky/go/src/github.com/JetBrains/teamcity-webhooks/webhooks-server/src/main/java/jetbrains/buildServer/webhook/async/AsyncEventDispatcher.java:[8,58] package jetbrains.buildServer.serverSide.impl.events.async does not exist
...
[ERROR] /Users/ricky/go/src/github.com/JetBrains/teamcity-webhooks/webhooks-server/src/main/java/jetbrains/buildServer/webhook/async/AsyncEventDispatcher.java:[55,13] method does not override or implement a method from a supertype

In my TC installation, I was able to find some JAR's which seem relevant (servlet-api.jar, openApi-source.jar), and it seems it should be possible to use these as dependencies for the build. However, it is not clear how to do so. Any guidance would be appreciated. Also, this is information that could be added to README.md. Alternatively, publishing a .zip with releases could be an option.