Env to check for assert

Use the env LKT_NO_ASSERT to disable asserts in lektord and lkt. Make a function pointer named lkt_assert which will be set to assert when LKT_NO_ASSERT don't exists or when the value is an empty string.

Do something like this:

void
__no_assert(int _true)
{
    (void) _true;
}

void
__yes_assert(int _true)
{
    if (!_true) {
        LOG_CRITICAL("Assert failed");
        exit(EXIT_FAILURE);
    }
}

void (*lkt_assert)(int);
/* extern void (*lkt_assert)(int); in header file */

void
lkt_set_assert_mode(void)
{
    char *no_assert = getenv("LKT_NO_ASSERT");
    if (NULL == no_assert || strlen(no_assert) == 0)
        /* __yes_assert */
    else
        /* __no_assert */
}