Rendering exceptions are now shown in event log.

I had some problem with UTF-8 handling on Windows platform. This showed me a problem with the Semaphore handling on exceptions when rendering asciidoctor. 

I added a special hint for encoding problems (probably windows platform only) on how to start the IDE. Adding `-Dfile.encoding=UTF8` to `idea.exe.vmoptions` fixed the problem for me. I hope this will no longer be necessary with a more recent JRuby version due with Asciidoctor 1.5.2