Adds ability to query by comment_author to WP_Comment_Query
Creates global instantiation of WP_Logger
Removes register_plugin and adds register_plugin_email

Adding plugin taxonomy term is now handled directly in add_entry to
minimize the actions required for a developer to begin logging
messages.
Adds sanitization directly within prefix_slug
Modifies add_entry

Log (post) parameter is now always a string instead of being a WP_Post
object.  Term is now created in add_entry if not already set,
minimizing the number of steps for a developer to use WP Logger. Adds
failure checks and updates method docs.
Updates method docs for get_entries