Add WP-CLI commands - shared-counts display, shared-counts popular, shared-counts update

[richardbuff]

Add WP-CLI functionality

wp shared-counts display 123
Display shares for single post

wp shared-counts popular --count=100
Display most popular posts

wp shared-counts update 123
Update share counts for a single post

Screencast of these three commands in action:

https://share.getcloudapp.com/z8ux9L4D

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (modification of the currently available functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project (WordPress coding standards, etc).
• My code has appropriate phpdoc comments with a description, @since, @params and @return.
• My code is tested for both new installs and for users that are upgrading from older versions.

[billerickson]

Looks great to me! Here are some recommended changes:

• Change wp shared-counts display to wp shared-counts get
• In the popular subcommand, set the default posts_per_page to 20, matching the dashboard widget
• In the popular subcommand, make the first column Post ID and the second column Title
• Consider using the table output style for the get and update subcommands, matching the popular one.