Praetorian-cli

- [Bug] Fixed an error with the `list` and `search` commands.
- [Misc] Additional status of 'P', 'PL' have been added for assets.

- [Breaking change] The `D` status for risks is expanded to `DE`, DI`, `DL`, `DM`,
`DH`, and `DC`for the severity levels of exposure, info, low, medium, high, and
critical.`D` is no longer a valid status for risks
- [Misc] Improved in-app documentation, where the `--help` text includes
more example usages.

- [Bug fix] Fixed errors in functions related to principals in
the Accounts class

- [Breaking change] `username`, `password`, `client_id` instance
attributes of the `Keychain` class are now accessed by functions
of the same names, ie, `username()`, `password()`, and `client_id()`
- [Breaking change] `api` instance attribute of the `Keychain`
class is now accessed by the `base_url()` function
- [Breaking change] 'T', 'I', 'R', and 'O' are no longer valid
statuses for risks