This adds a Flush method to the DB interface so that users of the DB
type can flush the underlying database to disk as needed.
The immediate use case for this is to allow for flushing dependencies.
For example, the block database always needs to be flushed to disk prior
to the UTXO database being flushed to disk to ensure that the UTXO
database remains in a recoverable state in the event of an unclean
shutdown.
This introduces a new interface named BlockSerializer and updates the
functions that currently take a pointer to a dcrutil.Block struct to
accept the interface instead.
This removes the tight coupling between the two packages at the API
boundary and allows callers to easily provide custom values.
Since the interface is already implemented by dcrutil.Block, no further
changes to the code or tests is needed.
This merge commit adds the following code from the
github.com/decred/dcrutil package into a new
github.com/decred/dcrd/dcrutil package:
* Address handling
* Amount type
* AppDataDir func
* bitflags functions
* Block wrapper type
* Hash160 func
* Tx wrapper type
* WIF type
as well as all tests for this code.
The old github.com/decred/dcrutil/hdkeychain package has also been
merged and moved to github.com/decred/dcrd/dcrutil/hdkeychain.
dcrd packages have been updated to use the new packages and the dep
files have been updated for this change.
