first pass at ditching wp-admin/setup-config.php
core config: abort if wp-config.php already exists
core config: check DB credentials
core config: update man page

[ci skip]
Merge pull request #484 from wp-cli/config-extra

Add --extra-php flag to `wp core config`
move Utils\set_user() to Runner::set_user()

it's not a general-purpose utility and it shouldn't be public
extract find_command_to_run() method
make load_command() and load_all_commands() standalone utilities
`$group` is optional for the function, so let it be optional for the command too
Regenerate cache man
Merge pull request #485 from wp-cli/cache-delete-optional

Allow <group> to be optional for wp cache delete
core config: fix notice when not passing --dbpass
core config: set WPLANG based on downloaded locale

fixes #488
bump version to 0.10.0-beta