DATAMONGO-856 - Documentation updates.

Updated references from springsource.org to spring.io. Updated references to mongodb.org. Update vendor to Pivotal Software, Inc. Update required/recommended versions. Update CustomConversions configuration section. Added missing section id's. Fixed some typos. Added missing JavaDoc.

Original pull request: #128.
DATAMONGO-856 - Documentation update.

Removed outdated why-spring-data-doc. Removed CouchDB reference from requirements document. Fixed some typos. Added missing opening <para>-element. Fixed rendering of author information. Added copyright and product name information.

Original pull request: #128.