Support for defining the select part for a column (ActiveRecord only for now)
Merge branch 'master' into sql_select_option
Changed api for column that accepts a query
refactor of defining a value as sql
Merge branch 'sql_select_option' of https://github.com/iwiznia/datagrid into iwiznia-sql_select_option
Merge branch 'master' of github.com:bogdan/datagrid

Conflicts:
	lib/datagrid/columns/column.rb
	spec/datagrid/columns_spec.rb