Resolves #422
Resolves #606

Related to GH-422 and GH-606

This commit effectively a merge of work with #607 and simplifies the following
- CloudEventAttributesProvider now provides CloudEventAttributes initialized with defaults to be set by the user
- In HTTP RequestProcessor the logic of sanitizing headers was improved to ensure that correct prefix is applied

Resolves #607

Related to #422,606

Normalizing in this context means converting it to binary-mode so the rest of the processing logic is the same.
Added support for canonical attribute names. Now, internally any attribute can be set as 'ce_' regardless where it came from are where it goes to as the frameork will be able to recognize both
Removed CloudEventMessageConverter
Renamed CloudEventAttributes to CloudEventAttributesHelperas it is better suited to what it actually does

Related to #422 and #606

Related to GH-422 and GH-606

Related to GH-422 and GH-606

Added CloudEventAttributesProvider and default implementation
Added CloudEventMessageUtils

GH-422 Formalize Cloud Event conversion strategy to consistently handle binary-mode and structured-mode cloud events

Moved CloudEvent related artifacts to ‘cloud events’ package with hopes to eventually donating it to CNCF SDK
Created CloudEventUtils identifying necessary constants and utility methods

Added initial README
Polished tests

This commit adds initial set of samples and tests demonstrating various ways of how cloud event can be consumed (i.e., structured, bindary, pojo etc)

Added initial implementation of MessageConverter
At the moment there seem that MessageConverter(s) would be the only thing needed to integrate Cloud Events with various elements of Spring

Resolves #592

This initial fix ensures that functions can process single MultipartFile as well as multiple.

Resolves #597