test: Add unit test for column_list
groonga: Implement column_list command
groonga: Add column_list to the list of generic commands
groonga: Return columns with a header
groonga: Don't output WITH_WEIGHT twice
Fix mismatched constant name
Fix syntax error around case-when statements
Fix typo
groonga: Spearete operations
groonga: Fix wrong class path to "Groonga" defined by Rroonga
Fix typo
test: Fix expected result of column_list
test: Fix test cases for column_list command
Output error message in the result
groonga: Don't return "false" as the result of error message
test: Don't assert erorr message