v0.1

First version of the plugin. It allows:

• Adding one or multiple key/value pairs to a page's metadata.
• There are two modes for adding metadata (visible/invisible). In visible mode, the "value" of the declaration will be part of the text displayed on the page. In invisible mode, the entire metadata declaration will be hidden.
• By default, metadata is stored as a string, but it can be specified to be stored as an integer or as a Unix timestamp.