Refactor xml_request API

Old API was bothering me. Make it match run_request more closely.
Add S3 debugging mode (dump request/response)
Tests for key accessors
bucket create and destroy

Bucket ACLs currently left unimplemented; I'll return to this later.
some POD syntax fixes
drop xmlns

Amazon isn't even consistent about what the correct namespace is, and they don't seem to mind if it's missing. Stop sending one.
Fix some warnings (mostly undef values)
Add Key->signed_uri
Fix time zone mismatch