Allow mailers other than gmail and accept ruby hash for configuration options

I don't know how necessary these changes are but I figured I would offer them up.

I needed a way to specify the mail server and domain (since we aren't using gmail).  So I modified the mail config to accept more options.

I also modified the path_to_config to also accept a Hash so that you can do things like:
```ruby
databases = ActiveRecord::Base.connection.execute("show databases;").to_a.flatten - ["information_schema", "mysql", "performance_schema", "test"]
default_options = YAML::load_file(Rails.root,join('config', 'backup.yml'))
databases.each do |db|
  S3MysqlBackup.new(db, default_options.merge(backup_dir: "path/to/backup/#{db}")).run
end
```