Updates ignore list to remove the old 'github-wordpress-plugin.zip' archive file exemption.
Applies source formatting.
Updates to support setting a user-configurable value for the plugin shortcode.

While the settings page works now, and properly validates and persists the user-specified shortcode, the plugin still uses a hard-coded shortcode value. This will be changed shortly.
Updates names of shortcode setting input to remove test input references.
Adds new OptionsManager class.

This class provides a simple convenience utility for accessing plugin options, and filling in a default value for the plugin options when no user-configured values exist.
Updates to use the new user-configuration shortcode name for the registered shortcode for this plugin.