Error if no encoder is set
Set the default field name of the message field back to 'message' for LogstashFormatter,
but leave it as '@message' for  LogstashAccessFormatter.

This ensures backwards compatibility for the default field names for both formatters.
Add Edu Garcia to contributors
Add note to README.md about logstash access field names
Add some minor javadoc
Merge branch 'Arcnor-master-53' for pull request #53
Add ability to suppress fields in the output
Merge branch 'optional_fields'
Add ability to customize JsonFactory and JsonGenerator.

Decorate JsonFactory when the formatter starts.

Also delay parsing of the customFields until after the formatter starts,
to ensure JsonFactory is properly decorated first.

Simplify LogstashMarker interface by just using the ObjectCodec (ObjectMapper) from the JsonGenerator,
rather than passing a separate ObjectMapper instance.

Unit tests and documentation for decoration.
Merge branch 'json_factory_access'
Merge branch 'encoder-issue'
Fix newline for WINDOWS
[maven-release-plugin] prepare release logstash-logback-encoder-3.3
[maven-release-plugin] prepare for next development iteration
Update README.md