auto auth, r session functions, resumable uploads

• Fix bug where you can't rename objects via name in gcs_upload
• Add gcs_save to store R session data in cloud
• Add gcs_load to restore session data stored with gcs_save
• Fix resetting of options(googleAuthR.rawResponse = TRUE) when using gcs_get_object
• Add URLencoding to object_name in gcs_get_object etc.
• gcs_global_bucket and gcs_get_global_bucket to set global bucket name
• Add options to set environment variables for API keys, default buckets etc.
• Add print S3 methods for objects, buckets and ACL
• Add option to use your own write function for R object file uploads in gcs_upload
• Add option to include object metadata in uploads via gcs_metadata_object
• Add resumable uploads to gcs_upload to allow uploads over 5MB, limit now 5TB
• Add retry uploads via gcs_retry_upload
• Add delete object via gcs_delete_object
• Add gcs_source to source .R files from GCS
• Add versioning and lifecycle management to create and update bucket functions