Networth

- add metals.live data service

- clean up and minor refinements.

- Add *estimated value overrides file* setting.
- Add --details option
- Add --write-data option
- Add plot-networth command
- Allow categories to be specified for downloaded token prices.

- Add support for downloading prices of precious metals.
- Switch to *NestedText* for the settings files.

- Now uses `QuantiPhy Eval <https://github.com/KenKundert/quantiphy_eval>`_ to allow you to use expressions within strings for estimated values.

Convert to using new IEXcloud API for downloading security prices.