Add Support for "event_name" field for MetadataMatcher in InMemoryEventStore

[fjogeleit]

I have a Prooph\EventStore\Projection\Query wo is using a MetadataMatcher for the MessageProperty event_name (Using PostgreSQL EventStore`.

When I try to test this Query local with a InMemoryEventStore this MetadataMatcher is not working because this field is only supported as messageName / message_name.

To make this test possible this PR also add support for the event_name as field name in the InMemoryEventStore

[fjogeleit]

The second commit is only for updating the comment section to pass the Travis CI checks

[coveralls]

Coverage increased (+0.001%) to 99.01% when pulling 09e92fd on fjogeleit:7.x into 1aac955 on prooph:7.x.

[prolic]

Why do you refuse to use message_name?

[fjogeleit]

Because message_name doesn't work in productive for a PDO based query. It's generating a where clause like message_name = :value but the field name in the PDO EventStore is called event_name. So its thrown an exception.

With this change I can use event_name in production with a PostgresEventStore in my case and also in my tests with an InMemoryEventStore