Add support for setting terms in batch

[bobbingwide]

The logic to create letter taxonomy terms should work when the code is being run in batch.
This is needed when parsing the source code in oik-shortcodes for WP-a2z.org and oik-plugins.

Expected output

Letter taxonomy terms set for posts created or updated in oik-batch

Actual output

Letter taxonomy terms were not being set.

Explanation

The lazy logic was not being loaded since $_REQUEST['tax_input'] was not set.

Solution

Check for Command Line Interface.
In the lazy loaded code cater for $_REQUEST['tax_input'] not being set.

[bobbingwide]

It appears that the check for command line interface works better if you call php_sapi_name() rather than test the value of the PHP_SAPI constant. See bobbingwide/oik-batch/issues/19