Correct the omission of solutionSize from the block header format, and document that compactSize uintencodings must be canonical.
Correct the omission of solutionSize from the block header format, and
document that compactSize uintencodings must be canonical.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips