Add section for prepared statements.
Add more sections to database docs.
Add notes about new ORM to migration guide.
Finish off database-basics section.
Start table object + entity docs.
Use methods instead of properties.

Add a section about the TableRegistry as well.
Update language in migration guide.
Corrections based on feedback.
More corrections from review feedback.
Merge pull request #891 from cakephp/3.0-database-docs-pt2

3.0 Database docs pt2