* `SecretBytes` and `Scalar` now take ownership of data when creating them (`mut data: T`), rather than taking a mutable reference (`data: &mut T`) and zeroizing it
* Removed unused variants of `RpcError`
* Added some convenience functions
* Renamed some things:
    * Renamed `get_spend_seed()` to `get_stealth_spend_seed()`
    * Renamed `get_view_seed()` to `get_stealth_view_seed()`
    * Renamed `STEALTH_PREFIX` to `STEALTH_ACCOUNT_PREFIX`
* Added tests
* Bug fixes
* Tweaked features
    * Disabled `rpc` by default
    * Disabled `stealth` by default (it was accidentally enabled by default, contradicting `README.md`)
    * Added `all` to easily enable all features (currently only `rpc` and `stealth`)