Minify 2.0.0

• Rename plugin and move under Pelican Plugins organization
• Restructure according to latest plugin best practices
• Add JS_MIN setting and ability to minify JavaScript files
• Replace all minifiers with minify-html

Minify 1.0.0

Breaking: Plugin is now referred to as pelican.plugins.minification in PLUGINS.

Huge thanks to @ysard for the refactoring and improvements!

See the changelog for details about the changes.