Added DDL section
Added Literal vs. Expression to SQL section
Fixed formatting of class, variable names in DDL ans SQL pages
Fixed DDL imports
Fixed note section in SQL section
Merge pull request #870 from ralphschindler/feature/ddl

[WIP] Zend\Db additions
[#870] Incorporate feedback, edit

- Incorporated feedback
- Fixed tables
- Minor grammatical/flow edits
Merge branch 'hotfix/870'

Close #870