[Keep] Improve speed of /index requests
|Velocity based estimate||-|
/index on a large production machine takes well over a minute to complete.
This could be a result of having to
stat() each file in order to get the modification timestamp.
Additionally, the IndexHandler currently builds the entire response in memory before writing the response to the user. To minimize client timeout issues, it should emit each file as it is found, or one prefix-directory at a time.