Changed class name from content to extruder-content

I have used your plugin and I find it quite awesome. However, I found an issue that definitely needed attention. You do create a "div" tag with a class name "content". Using a class name "content" is rather unsafe since many web developers have a "content" class name within their code especially in CMSs that have "content" class name in many sections of their code. This would make a mess of ones work when JavaScript affects your plugin's "div" tag of class name "content". I made changes to your plugin code and replaced the class name "content" with  "extruder-content".