We added --frontend-http2-window-size,
--frontend-http2-connection-window-size, --backend-http2-window-size,
and --backend-http2-connection-window-size option to replace existing
*-bits options.  The old options are not flexible because they only
specify number of bits.  Now we can specify integer value, with
possible g, m, and k unit.  The old options are still available for
backend compatibility, but are deprecated.