Merge pull request #869 from wp-cli/comment-meta-command

Implement `wp comment meta`
Use new public methods of `\WP_CLI\Runner` to set the `url` if it was passed as an assoc arg by prompting.
avoid leaking private \WP_CLI\Runner properties and methods
implement `wp cli info --format=json`
fix 'Warning: unknown --info parameter'
implement 'wp post generate --post_content=<content>'
Merge pull request #879 from wp-cli/wp-cli-ssh

Do something about wp-cli-ssh
Merge branch 'master' into fix-global-prompt-805
Introduce `\WP_CLI::set_url()`, which will set the URL context for the execution.
Use the new `set_url()` method introduced in ab45bfd
Move these methods to where they should be
Test install via prompting
Introduce a helper method for launching a new WP-CLI process using the same context as the current process.
Now that we have a method to launch new WP-CLI processes, use it to flush rewrite rules after setting the structure.

Fixes #814
Support for filtering plugin and theme lists based on object attributes.
move parse_url() to utils.php, since it's a standalone utility
Test filtering based on object attribute
Merge pull request #805 from wp-cli/fix-global-prompt-805

Prompting doesn't properly set config values
These arguments should be optional
Call the PHP binary directly, and ensure all arguments are escaped