Removing gnuplot as a build dependency to allow use of buildhosts that do not have gnuplot installed.
Adding support for Cache-Control: no-cache headers as well as Accept: (mime-type) headers to set requested content type.
Adding support for explicit (non-interpolated) aggregation functions.  Modifying Span iterators to optionally skip interpolated values.  Modifying downsamplers to use shared interval windows.