add support for ddog events
add test binary
fix package ref
fix imports
add event type and source
update the test binary
add comments, drop the test binary
update README example
don't mess with Client.Namespace
Use AlertType constants of type string

This avoids the need for a String() function.
Add tests for Success, Info & Error
Use 'EventOps' to encapsulate detailed options for the event API

Clients can still use the simpler Info, Error, etc. abstractions for
common cases. If more metadata is required on events, clients can use
the more flexible (yet more verbose) Event.
Reject events larger than 8KB
Merge pull request #4 from andrei-m/add_events

Add event support