Added YARD documentation for recipes

A lot of hacks and wtf-code, maybe will refactor it some day. But... Doubt it :-)
Updated comments for tasks

Performed minor refactoring for `host` tasks
Added "host_task" to perform tasks on behalf of root user
Added nginx:enable and nginx:disable tasks
Fixed for thin recipe
Renamed deploy:cold to deploy:initial
Tweaks for mysql and postgres recipes

* mysql recipe can now pass mysql-root password to server
* mysql and postgres don't create database_config file if create_user fails
Use fetch(:variable, default)

instead of `variable || default`
Don't run monit:setup and nginx:setup after deploy:setup