adds support for Travis
set python version for travis to 2.7 only
Update README.md

Added Travis badge
Added support for setting custom headers for files uploaded to s3.
Updates issue #7 - Brings back S3_USE_CACHE_CONTROL setting and fixes
some documentation issues.
Updates issue #7 - Set old S3_CACHE_CONTROL in S3_HEADERS on init and
doc fixes.
Check for S3_USE_CACHE_CONTROL boolean
added S3_CDN_DOMAIN support
added tests for S3_CDN_DOMAIN support
added name to CONTRIBUTORS