Support piping of config files addressing.

This addresses issue #43 . As discussed in that issue thread, the next phase will be integrating sending of configs/content to the workers via IPC, but we could probably use a fresh issue for that. Also, the owner of parsons said he could not yet add in my change[implementing json parsing from a file pointer], because he is working on stuff in dev and planning on rolling out that feature later in October instead of right now. This is why this code implements file content extraction into a string and then the json gets parsed from it.
And right after the loop start do something like this:

```C
do
  r = read(fd, buffer + off, buffer_len - off);
while (r == -1 && errno == EINTR);
if (r <= 0) {
  err = bud_error_str(...);
  /* dealloc all stuff and return err */
}
```