In cases where we want to be able to decode a string that
is known to be a unified address, it doesn't make sense to have
to route through KeyIO::DecodePaymentAddress and then return
an error depending upon the result type, when it's possible to
provide unified address parsing more directly.
KeyIO::DecodePaymentAddress has been modified to delegate
to UnifiedAddress::Parse
The presence of this variant results in a situation where more
of the code than necessary needs to be aware of and handle
decoding failures. This change moves all handling of decoding
failures to the point of decoding.
The wallet now only stores Sapling extended spending keys, and thus can
only be used with keys generated from an HDSeed via ZIP 32.
Note that not all Sapling keys in the wallet will correspond to the
wallet's HDSeed, as a standalone Sapling xsk can be imported via
z_importkey. However, it must have been generated from a seed itself,
and thus is more likely to be backed up elsewhere.
libzcash::PaymentAddress has been renamed to libzcash::SproutPaymentAddress,
and a new typedef boost::variant is now libzcash::PaymentAddress. Similarly
for ViewingKey and SpendingKey.
A new class InvalidEncoding is introduced as the default boost::variant
option for each address and key type; it is used during decoding instead
of boost::optional.
All address and key storage functions in the wallet have been modified to
refer specifically to the Sprout types, as they are used very precisely.
In most other cases, the more general type is leveraged as much as possible,
and we convert to the Sprout type when necessary. This will be subsequently
wrapped in, or replaced with, context-specific functions once Sapling
types are implemented.