Rather than using bytes.NewBuffer, which is a read/write entity
(io.ReadWriter), use bytes.NewReader which is only a read entitiy
(io.Reader) in all cases where it is possible. Benchmarking shows it's
slightly faster and it's also technically more accurate since it ensures
the data is read-only.
There are a few cases where bytes.NewBuffer must still be used since a
buffer with a known length is required for those instances.
The genesis blocks are not really part of the wire protocol rather they
are part of a network parameters. Thus, this commit moves the all of the
gensis blocks and tests to the btcnet package.
Also, create variables in the test package for the mainnet genesis hash,
merkle root, and coinbase transaction for use throughout the tests since
they the exported values are no longer available.
This commit adds tests for the error paths when encoded and decoding
MsgHeaders. Also, while here modify the casing of the local vars to be
consistent.
