Feature Request: Automatically figure out content type of files being uploaded

[tcoulter]

Feature Request: The Ruby library should automatically figure out the content type of files being uploaded, where possible.

Problem: When calling create_file, you must specify a content_type option as part of the last parameter (a hash). This is annoying as for many cases it can be done automatically.

Proposed Solution: When no content_type option is passed, we run the file through this gem and see if we get a match: https://github.com/halostatue/mime-types