set task's delegates to nil on dealloc
ensure all delate methods are called on the main thread
fix memory leak
check to see if already cancelled before cancelling
added s3FileKey property to allow client to set the destination file key in the bucket
made file publicly viewable by adding canned ACL to upload request
hack to fix NSInvalidArgumentException crash from crittercism.

NOTE this does not fix the underlying cause which is likely to be a dangling delegate pointer.
convert to arc
remove tasks instance variable and use queue to cancel operations
remove weak ref
reduce timeout
add abort upload back to cancel
make sure we only cancel our tasks
Merge pull request #2 from nbransby/master

Improvements to fix leaks and convert to arc