Use separate methods for cleaner and simpler code
Use separate methods for cleaner and simpler code

 - For chunked upload, add `upload_part()` to handle one chunk upload
   and `upload_part()` now calls `upload_part()`.

 - For normal upload, move the code into `contiguous_upload()`

felliott/waterbutler,CenterForOpenScience/waterbutler,RCOSDP/waterbutler