The GitHub plugin will be responsible for sourcing the following types of information:

Nodes:

• Pull requests
• Issues
• Issue comments
  n.b. the body of an issue (or PR) is treated as its first "issue comment"
• Commit comments
• Review comments
• GitHub user identities

Edges:

• authorship
  users author the other nodes, e.g. user authors commit
• containership
  issues and pull requests contain comments
  (might merge with reference below)
• reference
  comments can reference other nodes, e.g. the line below where this issue comment references PR-35

This is based off the overall plugin architecture design (#26); implementation has started in 'Add types for GitHub plugin' (#35)