Requests for comment/ChangesList formatting

structure

 * ChangeLine (interface)
 * OldChangeLine
 * EnhancedChangesUngroupedLine
 * EnhancedChangesBlockGroupLine
 * flags
 * EnhancedChangesGroupNestedEntry
 * ChangeLineFormatter (interface)
 * OldChangeLineFormatter
 * EnhancedChangesBlockGroupLineFormatter
 * EnhancedChangesBlockGroup
 * EnhancedChangesBlockGroupSummaryLine
 * arrow
 * flags / timestamp
 * change summary
 * EnhancedChangesBlockGroupLine[]

hooks

 * EnhancedChangesCacheGroupingKey