DDC-3049: [GH-988] Exporter support for association fetch modes

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of holtkamp:

Url: #988

Message:

As reported here: http://www.doctrine-project.org/jira/browse/[DDC-3047](http://www.doctrine-project.org/jira/browse/DDC-3047)

Also noticed the fetch modes were not supported for PHP and YAML exporters.

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-988] was closed:
#988

[doctrinebot]

Comment created by @guilhermeblanco:

Merged as of 4029dc2

[doctrinebot]

Issue was closed with resolution "Fixed"