Improvements to `wp term` output

* Add `--porcelain` argument to `wp term create`
* `wp term create` should include term ID in success message
* `wp term delete` includes the term ID of the deleted term
* Updated tests / doc

See https://github.com/wp-cli/wp-cli/issues/399#issuecomment-16685216
Balance ze curly braces to meet WP standards

https://github.com/wp-cli/wp-cli/pull/407/files#r3886566
Merge pull request #407 from wp-cli/term-create-porcelain

Improvements to `wp term` output