Problem: encodes nothing if a UUID field is null

This means the encoded message is invalid, which is meaningless.

Solution: if a UUID field is null, encode as all-0 bytes so that the
message can be read safely.

Fixes #76
Merge pull request #77 from hintjens/master

Problem: encodes nothing if a UUID field is null
Added init script
Merge pull request #78 from mvala/master

Added init script
Updated readme with hint for the create script