This leads to two different formatters both called
JsonEventFormatter, just in different namespaces. That probably
wouldn't cause too much ambiguity, as few applications would depend
on both packages. It avoids longer names such as
"SystemTextJsonEventFormatter" which is pretty unwieldy.
Both the implementation and the tests are very much based on the
Newtonsoft.Json implementation.
Fixes#42.
Signed-off-by: Jon Skeet <jonskeet@google.com>