Added command-line timeout -t <sec> to restconf
Example: Added programmable timeout to backend example
Test: updated for fcgi and native using internal timeouts
* This is an experimental implementation
* Added `www-data` feature and two new config options to clixon-config.yang:
* `CLICON_WWW_DATA_PATH`
* `CLICON_WWW_DATA_ROOT`
* The limited implemtation is as follows:
* path: Local files within `CLICON_WWW_DATA_ROOT`
* operation GET, HEAD, or OPTIONS
* query parameters not supported
* indata should be NULL (no write operations)
* Limited media: text/html, JavaScript, image, and css
* Authentication as restconf
Generic changes:
* Uniform path selection across fcgi, native http/1 + http/2
* `201 Created` for created resources
* `204 No Content` for replaced resources.
* See [RESTCONF: HTTP return codes are not according to RFC 8040](https://github.com/clicon/clixon/issues/56)
* HTTP `Location:` fields added in RESTCONF POST replies
* Both a "native" stream support and one using nginx/nchan pub/sub.
* See (apps/restconf/README.md) for details.
* clixon-config YAML file has new revision: 2018-10-21.