Merge pull request #3 from Tpt/snak

Implement Snak serialization and unserialization
Add test for catching EntityIdParsingExceptions
Merge pull request #4 from wmde/snakDeserPropIdExceptionTest

Add test for catching EntityIdParsingExceptions
Merge commit 'b17c02d2cd9ed4a97c73cef87421a06d5cf6e2d5' into claim
Adds mock of SnakSerializer in tests