SanitizedFile should support read with an optional length and output_buffer arguments

[jcoyne]

Then it would conform to the IO api as documented here: http://ruby-doc.org/core-2.2.2/IO.html#method-i-read

Presently if I have this code:

cwf = Carrierwave::SanitizedFile.new
out = File.new
IO.copy_stream(cwf, out)

Then I get this error:

     ArgumentError:
       wrong number of arguments (given 2, expected 0)
     # /Users/jcoyne/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/carrierwave-0.11.2/lib/carrierwave/sanitized_file.rb:157:in `read'

[janko]

@jcoyne I remember two years ago trying to change CarrierWave::SanitizedFile#read to conform to the IO interface, because I wanted to build a Flickr storage gem, where the Flickr client used Faraday which required these two arguments. When I made changes that I thought could work, a lot of tests were failing for unknown reasons, and I think some of the failures were non-fixable. And it was a bit intimidating that CarrierWave::SanitizedFile can have so many states, which #read also changes. It really can be this simple.