libcdb-cli: add --offline-only, refactor unstrip and add fetch parser for download libc-database

[the-soloist]

1. make unstrip as default behavior, except file parser
2. add return_raw for search_by_symbol_offsets
3. add fetch arg parser to download and update libc-database

[peace-maker]

It's weird to run libcdb fetch and have the command do nothing. Maybe do the update by default and ask if you want to clone/init first if the directory is still empty?

[the-soloist]

I think init and upgrade repository is better, and remove --init.

[peace-maker]

Now the second time you run libcdb fetch it does nothing. I'd remove all arguments and just update the database if it exists and install it first if its the first time you run the command.

[the-soloist]

Sorry, I didn't quite understand. Currently, the expected behavior of second time run libcdb fetch will upgrade the repo.

If we want update database, we should pass -u

fetch_parser.add_argument(
    '-u', '--update',
    metavar = 'update',
    nargs = '*',
    choices = ['all', 'ubuntu', 'debian', 'rpm', 'centos', 'arch', 'alpine', 'kali', 'parrotsec', 'launchpad'],
    help = 'Fetch the desired libc categories'
)

like libcdb fetch -u ubuntu

First time run libcdb fetch or database path didn't exists, it will ask if you want init repo.

[the-soloist]

Setting a default value for -u meet your requirements?