Output a list of users as CSV or JSON with a new CSV helper utility
If only --ids are requested, we don't need to do anything else
Simplify the code to generate CSV and JSON output by typecasting. Feels a little dirty, but no harm no fowl.
Update man doc
Mention default output
Use the row we built to make sure we're only presenting data that correlates to headers
Use fputcsv with STDOUT instead of building our own CSV. Props @scribu
add some examples for user list and regenerate manpage
Reverse parameter order in output_csv() utility

... so that $headers can actually be optional.

Also fix coding standards violations.
Merge pull request #284 from wp-cli/user-list-csv

Output a list of users as CSV or JSON with a new CSV helper utility