lz4stream/block: compute block checksum on the block not its source.

Fixes #223.

Merge pull request #216 from evanphx/b-fix-tests

Reverts bc1239b, no longer needed to conform to legacy

Merge pull request #216 from evanphx/b-fix-tests

Reverts bc1239b, no longer needed to conform to legacy

Merge pull request #207 from honeycombio/lizf.copy4

Restore copyMatchTry4

Merge pull request #197 from greatroar/revert-hash5

Revert "Hash five bytes instead of six"

Merge pull request #188 from leehinman/flush_fix

remove state change after Flush

Merge pull request #180 from honeycombio/lizf.cherry-pick

cherrypick (#172): internal/lz4block: arm64 decoder improvements

Merge pull request #165 from greatroar/fix-160

Permit some invalid inputs in portable decoder