zsh via its ultra-tunable completions can do only 1st part of op's request i.e command option completion, but not the second part i think...

for example, i do the following:

    anupam@virat ~ % autoload -Uz compinit
    anupam@virat ~ % compinit
    anupam@virat ~ % git a<TAB>
    add        -- add file contents to index
    am         -- apply patches from a mailbox
    apply      -- apply patch to files and/or to index
    archimport -- import an Arch repository into git
    archive    -- create archive of files from named tree

edit-001: added trivial example.