So that "http_server.h" does not have to include "serval.h" which
creates a circular dependency.
Remove the __SERVALDNA__HTTP_SERVER_IMPLEMENTATION hack from
"http_server.h"
Change a test case: configuration options are now case sensitive.
Fix config file load and parse logic in conf.c, always copy 'debug' flags
from config.debug.
The config schema 'interfaces' option is no longer MANDATORY.
Introduce new CLIFLAG_PERMISSIVE_CONFIG to supress bad-config ERROR messages
from the 'config set' and 'config get' commands.
Refactor cli_execute() into cli_parse() and cli_invoke(). Use *const* struct
command_line_option everywhere.
SET_NONBLOCKING(), SET_BLOCKING(), WRITE_STR() are now set_nonblock(),
set_block() and write_str() respectively, all of which log an error before
returning -1. There are other useful methods: write_all() treats anything less
than all bytes written as an error; write_nonblock() treats EAGAIN and EINTR as
zero bytes written, and a combination: write_all_nonblock().
