Github-archive

- Fixes a bug that tries removing the authenticated user from a list so we don't double dip git operations even when there is no authenticated user (eg: using the `--https` flag)
- Fixes a bug that allowed users to use both the `--token` and `--https` when it should only be one or the other

- Adds a new `--fork` CLI arg which adds support to fork the repos or gists specified via `users`, `orgs`, `stars`, or `gists`
- Removed various shorthand CLI args to avoid confusion and improved help message output for CLI args (updated docs as well)
- Breaking Change Note: The previous `-f` flag that would include forks when cloning or pulling repos/gists is now associated with the `--fork` CLI arg which will actually fork repos to your account. The `--forks` (plural) CLI flag no longer has a shorthand option
- Namespaces for various functions changed for better project organization. As this project is intended to be used as a CLI tool and not a library, the impact should be minimal

- Clarifies default location of github-archive in help output

- Switches from the `threading` package to the `concurrent.futures` package allowing us to return values from each individual thread (in this case, the names of failed git assets)
- Fixes a long-standing bug where git repos that failed to clone would remain in the archive on Windows. This meant that recloning was impossible due to the repo existing and pulling was not possible because the repo wasn't yet fully initialized. The tool now has a proper cleanup step after everything has run that is compatible with both Unix and Windows environments (closes 38)
- Adds `--log_level` to allow the user to specify a custom log level
- Small adjustment to `include` and `exclude` help verbage used to be more clear they are optional filters

- Adds an `--include` and `--exclude` CLI flag that accepts a comma-separated list of repo names to either include or exclude. If neither are passed, no filtering will occur (closes 43)

- Adds the ability to specify a custom base_url for GitHub (useful for enterprise GitHub users with a custom hostname, closes 41)