Tessa

- Remove investpy because it is no longer working, see
https://github.com/alvarobartt/investpy/issues/600 and
https://github.com/alvarobartt/investpy/issues/610
- Add yfinance / Yahoo Finance support instead(simplifying a
number of things in the interfaces such as type_, country
and _querytype).
- Add the symbol functionality/interface, namely new classes
`Symbol` and `SymbolCollection`.
- Revamp search interface, now supports filtering and
bucketizing, returns Symbol objects. See new
`SearchResult` class for more information.
- Add much more comprehensive documentation.
- Revamp folder structure.
- Encapsulate everything related to sources in new `Source`
class. All symbols have a `source` attribute now.
(`source` attribute is roughly a replacement for the old
`type_` attribute.)
- Signatures of most/all `price_*` functions changed.
- Add a number of types such as `SourceType`,
`PriceHistory`, or `PricePoint` to make the code clearer
and help with autocomplete suggestions in the IDE.

Their rate limiting seems to have become more sensitive lately, triggering 429s with a 1 second timeout.

This will also make tessa work in Google Colab, see also 7.

- Enable the package to work w/ many more python versions.
- Resolves issues 7 and 8.

- Add `currency_cross` type.
- Make `bond` type work. Requires to workarounds (remove `country` param for bonds, return "UNKNOWN" as currency if that column is missing in the returned dataframe) because bond types have issues in investpy. See also https://github.com/alvarobartt/investpy/issues/572 and #5. Might later need to re-add the country for bond type when/if investpy gets fixed.

- Change MIN_FROM_DATE in investing from 01/01/1900 to 01/01/2010 so investing.com doesn't get hit with too many (sub)requests. Adjust MIN_FROM_DATE if you need data before 2010.
- Reduce the wait time for investing.com to 1s.
- Add "commodity", which was a missing type.
- Fix all kinds of minor issues.