There is no point to using time.Duration if the value is interpreted as
milliseconds. Callers should use the standard multiplication idiom to
choose the unit. In fact, the only caller outside of the tests already
does so.
Account is now always a non-pointer. This will be important once
the manager starts remembering accounts.
AccountManager is now always a pointer because it contains locks
and locks cannot be copied.
* Change account signing API to two sign functions;
Sign without passphrase - works if account is unlocked
Sign with passphrase - always works and unlocks the account
* Account stays unlocked for X ms and is then automatically locked
* Use crypto.Sign instead of directly calling secp256k1 lib
* Rename UserAccount to Account and Addr to Address (for consistency)
* Change AccountManager.Sign to take ptr to Account instead of
address byte array
* Simplify copying of Accounts in Accounts()
* PubkeyToAddress and GetEntropyCSPRNG now exported
* Add initial UserAccount and AccountManager structs
* Add NewAccount, Sign and Accounts functions
* Refactor key stores to use key address as main identifier
while keeping the UUID.
* Use key address as file/dir names instead of UUID
