Merge pull request #3 from bquorning/write_binary_file

Write in binary file mode
Merge pull request #1 from bquorning/minor_changes

Minor changes
AWS no longer escapes forward slash in the identifier
Use AWS subdomain when possible. Copied from CarrierWave 0.8.0
Implement #url as #public_url
Create an authenticated URL when needed. Copied from CarrierWave 0.8.0