HtmlLiveReporter optional ctor arg for specifying a report save filepath

I prefer to setup objects to have everything they need to do closer to they creation and then let them go.

* renamed reportPath property to reportTemplateUrl
* reportPath is now an optional Some(string) property where you can save the report
* The reporter on quit will save the html to the directory and file specified. 

I didn't like renaming the property but you are not 1.0 yet and I felt reportPath for a Url was confusing. I am open to not doing this.