- Bumped version 0.1.2 -> 0.2.0 (but to 0.2.0 means we broke the 0.1.x interface.)
- Added logic to Sidecar_Shortcode to monitor if posts have the shortcode and to store a value for "_sidecar_has_{$shortcode_name}_shortcode" in post meta.
- Prefixed the names of the functions used for action and filter hooks in Sidecar_Plugin_Base with an underscore ('_') to minimize chance for conflict in subclasses.
- Added a 'save_post' action to delete any  "_sidecar_has_{$shortcode_name}_shortcode" in post meta for the post. If the post is getting updated then we need a chance to reset them.
- Deleted a legacy block of code that had been commented out waiting for testing.
- Changed the "sidecar_print_styles" hook to be sidecar_print_{$this->plugin_name}_styles" instead so multiple plugins using Sidecar don't run the hook multiple times. We might need this technique in more places.
- Sets $used flag in Sidecar_Shortcode->do_shortcode() and then saves a 'yes' or 'no' value to post_meta for future use in Sidecar_Shortcode->the_content().