Implement `wp theme get --field=<field>`
Wordwrap the description
Introduce `show_single_field()` and `show_multiple_fields()`, helper methods for printing object data
Convert `wp theme get` to use new util function
Convert `wp comment get` to new util functions
Have `show_single_field()` logically persist the `--format` argument.
Run moar faster
Convert `wp user *` to new util functions.
Convert `wp site list` to new util function.
Method isn't used anymore
Convert `wp post *` to new util functions.
Remove unused methods
Simplify again
Introduce `wp plugin get`

Closes #796
`--field=<field>` support for `wp term list` and `wp term get`
This is a better format

See https://github.com/wp-cli/wp-cli/pull/795#issuecomment-25442654
Strings are strings
Merge pull request #795 from wp-cli/theme-get-field-795

`wp theme get` should accept a `--field=` arg