Allow initialization without config file

[HalosGhost]

At the moment, there are two init functions:

• lwan_init()
• lwan_init_with_config()

As a side-note, the naming convention of these functions is somewhat confusing. The first function implicitly reads from a lwan configuration file (with the same name as the binary being run). The second allows you to pass a configuration struct, and therefore should allow for not needing a configuration file to be present.

Unfortunately, using lwan_init_with_config() does not escape the need for a configuration file. Lwan still requires a minimal config file when using this function, roughly:

listener *:8080 {}

Ideally, using lwan_init_with_config() should escape any need for a configuration file. Perhaps a configuration file, if one is present, should still be honored (though I am unsure if that's actually preferable), but it certainly should not be required.

It looks like the specific culprit here is try_setup_with_config() (reproduced below for ease):

static void try_setup_from_config(struct lwan *l, const struct lwan_config *config)
{
    if (!setup_from_config(l, config->config_file_path)) {
        if (config->config_file_path) {
            lwan_status_critical("Could not read config file: %s",
                                 config->config_file_path);
        }
    }

    /* `quiet` key might have changed value. */
    lwan_status_init(l);
}

I am hoping this can be modified such that if config != &default_config, it skips the check for the config file path. Does that sound reasonable? Are there any assumptions I am making which mean this needs to be done in a different way or that this cannot be done at all?