This makes it easier to add new dependencies, without having to
manually edit the `aiken.toml` file.
The command is accessible via two different paths:
- aiken deps add
or simply
- aiken add
for this is quite common to find at the top-level of the command-line,
and, we still want to keep commands for managing dependencies grouped
under a command sub-group and not all at the top-level. So we're
merely promoting that one for visibility.
This is a bit cleaner, as the 'cmd/new' had many on-the-fly functions
which are better scoped inside this module.
Plus, it plays nicely with the std::str::FromStr trait definition.
rvcas