Move article "Using a Custom Document Class Mapper with PHPCR-ODM" from CMF docs

[wouterj]

The CMF has an article which belongs more in the doctrine docs imo. It's "Using a Custom Document Class Mapper with PHPCR-ODM". I suggest moving it to this documentation as it provides some usefull information

[dbu]

+1

[dbu]

@wouterj did you also add the article here or only drop it from the cmf docs?

[wouterj]

It's in the 'old toc tree' branch of the cmf docs, it's not yet removed

[dbu]

see #42