Improve windows first usage experience

The current getting started guide makes heavy use of the -e flag and the fact that "agent" is supposed by the logstash.sh script.
It was not the case in windows bat 

Also, I suppose most windows user will easily replace "bin/logstash" with "bin\logstash" however using single quote on the doc for -e will never work for them. Would you mind switching to double quote, at least in the getting started guide to ease the copy-paste testing.