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.
Let's make it in reverse `bud_error_t bud_read_file_by_fp(FILE* fp, char** out)`.