Added portfolio command with the following subcommands:
`positions`: list positions for 1 or more accounts, which can be closed. Shows position details such as P/L, greeks, indicators, etc.
`margin`: break down margin usage by position for an account; can be configured to warn for high BP usage
`history`: view previous transactions and filter by symbol, instrument, date, etc.
`balance`: view current balances for an account, such as net liquidity, cash, BP usage
**Full Changelog**: https://github.com/tastyware/tastytrade-cli/compare/v0.1...v0.2