Remove theme readme

Add semver dependency
Add base plugin object and test validation of plugin
Add base loading of default addons

Add mixpanel as default addon
Add method to load a list of plugins from generator options
Load plugins during generation
Add command line option "plugins"
Add resources to site build
Add call for hooks "init" and "finish"
Add global js interface for plugins and remove mixpanel
Trigger event on document when ready
Add option to change templates from plugin
Use complete assets folder for plugins
Fix #36: add mathjax plugin as default
Use mathjax plugin version 0.0.2
Change js interface for plugins and add configuration
Update default addons
Add option --pluginsConfig
Change plugins separator to ","
Merge pull request #123 from GitbookIO/feature/plugins

Fix #65: Plugins Architecture