Don't output variables using translation functions (i.e. _e)
Include file using full path for better compatibility.
Use cap (manage_options) instead of role (administrator) for restricting access.
Use plugins_url instead of the WP_PLUGIN_URL constant to allow the plugin to work from alternate non-plugin folder contexts.
s/wp_print_scripts/wp_enqueue_scripts/
For stipple_validate, create a new array of values and return that to avoid and unwanted values from sneaking in.
Prevent notices on settings page display and save and use better default values for options.
Save the value of custom_stipple_load_data as well.