util/table: create Column interface, rename impl.
util/table: rename Column#get => row
util/table: re-enable a truncation test.
util/table: re-enable a streaming test.
util/table: re-enable an underfull test.
util/table: Column interface turned out not to be useful.
util/table: Column: store name separately from actual rows.
util/table: Column: pad in main class instead of builder.