[COOK-3328] Refactor main.cf template and attributes

Signed-off-by: Seth Vargo <sethvargo@gmail.com>
Update CHANGELOG format
Fix whitespace
Fix README formatting
Version bump to v3.0.0
Bump devodd release
[COOK-3530] Move node['postfix']['relayhost'] to node['postfix']['main']['relayhost']

Signed-off-by: Seth Vargo <sethvargo@gmail.com>
[COOK-3116] Add SmartOS support

Signed-off-by: Seth Vargo <sethvargo@gmail.com>