cod should attempt to learn flag descriptions

[zachriggle]

For the basic case of Python argparse-based help menus, it would be useful if cod could also learn the description of the flag (or at least the first line of it).

Compare the following (from the Pwntools repo):

asm --help
usage: pwn asm [-h] [-f {raw,hex,string,elf}] [-o file] [-c context]
               [-v AVOID] [-n] [-z] [-d] [-e ENCODER] [-i INFILE] [-r]
               [line [line ...]]

positional arguments:
  line                  Lines to assemble. If none are supplied, use stdin

optional arguments:
...
  -n, --newline         Encode the shellcode to avoid newlines

Tab completion only shows the flags themselves, and not the helpful descriptive text:

% asm -<tab>
--avoid    --encoder  --infile   --run      -c         -e         -h         -n         -r         -z
--debug    --help     --newline  --zero     -d         -f         -i         -o         -v

The learned autocomplete should show something similar to what is provided with the default Git completion:

$ git --<tab>
 -- option --
--bare                -- treat the repository as a bare repository
--exec-path           -- path to where your core git programs are installed

Such that it might look like this:

$ asm -<tab>
...
-n --newline          -- Encode the shellcode to avoid newlines