Remove an extra newline
Leave the points hook descriptions empty by default

The user input is only used as an override.

See #46
Points hooks: set the instance number when fetching a handler

Introduces the public `set_number()` method to replace the private
`_set()` method. The number is set before the hook is returned by
`WordPoints_Points_Hooks::get_handler()`.

Brought about by #46
Points hooks: in the points_type() method use the current number by default

Spurred on by #46
Update points hooks descriptions and generate them dynamically if needed

See #4
Points hooks: introduce a get_points() method to get the points for an instance

See #4
Unit tests: split the shortcode test case

Create a separate test case for each shortcode instead.
Introduce the [wordpoints_how_to_get_points] shortcode

Fixes #4
Points hooks: clean comment logs on post deletion

Also updates the other log cleaning to only clean the correct logs.
Formerly, any logs with that meta key would be deleted. Now only the
logs of the correct type are cleaned.

Fixes #55