v0.6.0

Breaking changes:

• The names of generated GraphQL types are now capitalized regardless of the terminology.

New features:

• resolvers.resolveSourceTypes can now return a Promise.

Miscellaneous:

• SemanticGraph#toString now displays the number of triples in the graph.
• Triples with predicates not used by the lib are not stored in memory.
• Improved documentation.
• Improved tests.