Proposed header for hash id, taken from ethz-asl/aslam_posegraph#10
Inline implementation and tests for Hash ID.
Resolved comments of #56
Merge pull request #56 from ethz-asl/feature/hash-id

128 bit hash ids
Hash id deserialization from hexString.
Merge pull request #57 from ethz-asl/feature/hash-id

Hash id deserialization from hexString.
Merge branch 'feature/catkinization'