copy files from wp-includes/export verbatim
copy wp-includes/iterators.php to export/iterators.php
load Oxymel via Composer
load export classes via Composer
first pass at loading and using the export API

* replace --file_item_count with --max_file_size
* --verbose is ignored, for now
add _wp_export_build_IN_condition() helper
log each exported file path

had to copy over the whole WP_Export_Split_Files_Writer class.
remove --verbose parameter

The idea is to be reasonably verbose by default and completely silent
when --quiet is passed.
Restore af65fe41c8d3b9df3c1fb1461fddf92ac165fde5, which I accidentally overwrote :(
Added wp.bat to bin section of composer.json
set Oxymel to version 0.1.0
merge master into export-api branch
check wp-includes/version.php before loading WP
Merge branch 'master' into force-install-476
Improve `theme install` logic to support force-installing a specific version.

Previous `theme install` logic:

* Updates the theme if there's an update available.
* Installs if the theme isn't installed.
* Otherwise, assume the theme is installed.

New `theme install` logic:

* Don't do anything if theme is already installed and no `--version` specified.
* If `--version` is set and is different than what's installed, force install.
* Install if the theme isn't installed.
A Behat test for force-installing a plugin
Behat test for force-installing a specific version of a theme.
Mention why there's no break

See https://github.com/wp-cli/wp-cli/pull/476/files#r4981709

[ci-skip]
Merge branch 'master' into export-api
replace VerboseExportWriter class with 'wp_export_new_file' hook