Tagging release v0.6.0

Merge pull request #386 from barakmich/optional_path

Add SaveOptional() to save predicates if they exist, and add the

Merge pull request #237 from jf87/master

added example n-quad file for gremlin api description

Merge pull request #145 from kortschak/gremlin

Fix gremlin timeout handling

Merge pull request #92 from kortschak/names

Rename Check-ish -> Contains-ish

Merge pull request #27 from barakmich/master

Fix the build story