[GSoC] Unify ref-filter formats with other --pretty formats

Hi,

Below are some two queries concerning https://git.github.io/SoC-2019-Ideas/#unify-ref-filter-formats-with-other---pretty-formats

Q1)

In pretty.h & pretty.c: void get_commit_format(const char *arg, struct rev_info *); This function Parses given arguments from "arg", checks it for correctness and * fill struct rev_info.

In ref-filter.h & ref-filter.c: int verify_ref_format(struct ref_format *format); This function is Used to verify if the given format is correct and to parse out the used atoms.

Now, the verify_ref_format function can be used inside get_commit_format function, hence reusing logic. Is this a correct example to work on, for this project ? If not, please point out an example so as to understand the problem statement better.

Other than this I can't find any other example, for this project in pretty.* and ref-filter.* Perhaps some examples could be found in command specific files, right ?

Q2) About a recurring term 'atom' in ref-filter and pretty: what is atom ? is it a piece of a whole document ? and what is meant by used atoms ?

Thanks.