Batching, Service Accounts and Custom Configs

• Added ability to add your own custom headers to requests via customConfig in gar_api_generator
• Add 'localhost' to shiny URL detection.
• Google Service accounts now supported. Authenticate via "Service Account Key" JSON.
• Exposed gar_shiny_getUrl and the authentication type (online/offline) in renderLogin
• renderLogin : logout now has option revoke to revoke authentication token
• Added option for googleAuthR.jsonlite.simplifyVector for content parsing for compatibility for some APIs
• Batch Google API requests now implemented. See readme or ?gar_batch and ?gar_batch_walk for details.
• If data parsing fails, return the raw content so you can test and modify your data parsing function
• Missed Jenny credit now corrected
• Add tip about using !is.null(access_token()) to detect login state
• Add HTTP backoff for certain errors (#6) from Johann
• Remove possible NULL entries from path and pars argument lists
• Reduced some unnecessary message feedback
• moved with_shiny environment lookup to within generated function
• added gzip to headers