RMarkdown authentication and auto-package creation

v0.4.0

• Add client based authentication in JavaScript plus example app
• Add check to gar_auth_service to see if you have downloaded right JSON file
• Discovery API functions to get details on Google APIs added: gar_discovery_apis_list and gar_discovery_api
• Add gar_create_package that takes gar_discovery_api JSON and creates R package
• Change warnings() in batch to myMessage() level 2
• ensure batch requests only occur per second to help calculation of QPS limits
• Add 404 message if batch requests are not found.
• Fixed halt error if message can't parse body JSON, will now fail gracefully but carry on
• allow overwriting of default httr "encode" again (#28)
• Headers will contain up to date version number of package
• Add gar_auto_auth and gar_attach_auto_auth for auto-authentication upon a package load
• Fix bug where you couldn't pass in the file location of the ".httr-oauth" location to gar_auth()
• gar_auth now raises errors not NULL for passing incorrect token file locations of tokens
• gar_auth respects renamed .httr-oauth tokens now via getOption("googleAuthR.httr_oauth_cache")
• Add link to Github repo with auto-generated packages: https://github.com/MarkEdmondson1234/autoGoogleAPI