initial interface for a request hook, sample interface and example for logging
added filename to constructor
Don't pull the security token from the environment or config
when a caller supplies the access key and secret
Merge pull request #2123 from jimbrowne/security-token-env-ignore

Don't pull the security token from the environment or config when a caller supplies the access key and secret. Fixes #2123.
Merge pull request #2125 from dkavanagh/request-hooks

Add request hooks and request logger. Fixes #2125.