Quickclone

1. Detect missing configuration files and give user the option to create the
missing configuration files. (DONE)
2. Warn about configuration file encoding bugs. (DONE)
3. Pass extra command-line arguments to VCS command. (DONE)
4. Streamline main entry point. (DONE)

1. Fix syntax to be 3.7-compliant.
2. Move cache location from `~/.cache/quicktoml` to `~/.cache/quickclone`,
with prompt to user asking whether they want to move the old cache data over.

1. Add `-L/--last-clone` flag to get the directory of the last clone operation.

1. Add support for mercurial.
2. Allow overriding the `vcs.remote` configuration option using the
`-S/--system` flag. Currently, this flag accepts `git`, `mercurial` or `hg`.
3.

1. Add support for SCP-like locators (e.g. gitgithub.com:RenoirTan/QuickClone.git)
2. Add unit tests for most of the quickclone library.
3. Add `options.remote.force_scp` option to quickclone.toml.
4. Allow users to use a different config file instead of the one in `~/.config/quickclone.toml`
by using the `--config-file <path>` flag.