Add CloudFront filter plugin

Amazon CloudFront log files use the W3C extended format.
The files start with a header that describe the fields, like:
#Fields: date time sc-bytes c-ip cs-method cs(Host) sc-status cs(Referer) cs(User-Agent) cs-uri-query

The S3 input plugin automatically adds this as metadata to events.
This filter uses the metadata (or user-specified metadata) to parse the event fields.

With the S3 input pointed at the CloudFront log bucket, the filter should work without any specific configuration.