Octokit API calls: error handling and toggles

[cboettig]

• Should be able to toggle off all API calls using _config variables
• API call errors should echo error messages but not interrupt site building (?)
• API calls should echo progress (optionally?) in compile

[cboettig]

Octokit calls are a bit faster and more robust. Don't have proper error handling and toggles yet, but that's pretty much true for all my plugins.