threshold of quadratic and linear growth of CLIgen buffers (cbuf:s)
* Memory footprint
* Do not autopopulate namespace cache, instead use on-demand, see `xml2ns()`.
* Set CBUF start level to 256 (`CLICON_CLI_BUF_START` option)
* Reduced xml child vector default size from 4 to 1 with quadratic growoth to 64K then linear