* fixed a regression introduced recently: in certain cases, some fees related to conversions would no longer be generated (thus causing small deductions to be ignored)
* added support for USDC: previously it was conflated into fiat and didn't generate a tab, now it does
* Coinbase plugin: added support for fiat_withdrawal and fiat_deposit transactions. They are now tracked internally and no longer cause an unsupported transaction warning
* Coinbase Pro plugin: added support for "conversion" native transactions (these seem to occur when CBPro converts from/to a stable coin)
* minor changes to documentation