Allow wp-db-export to write to STDOUT if <file> is -
Update wp-db-export phpdoc options
Suppress success message when exporting to STDOUT
Make db-import accept - for STDIN

Note there seems to be no difference with db-query for this.
Merge pull request #898 from x-team/db-export-stdout

Allow wp-db-export to write to STDOUT if <file> is -