Improve config.database_names example using #pluck

ActiveRecord provides #pluck as a better way to get all the values from one column than Customer.select(:database_name).map(&:database_name), so I changed the README to use it instead.
Merge pull request #30 from codeodor/patch-1

Improve config.database_names example using #pluck
release 0.19.0
Merge branch 'development' into mysql_schemas
allow reload to take config
refactor the connection handling in tests
remove ActiveSupport delegation dependency
merge conflicts
excluded models for mysql schema adapter now use default db