Table of content issues

[carlosliu]

1. Data Mapper (line 1019) and Observer Pattern as an External Service (line 1095) should have #### in front of them, rather than ###.
2. Should Interpreter be a subsection of Directives? It's a pattern, instead of an AngularJS component. The DSL interpreter could be a part of directives content.

[mgechev]

Yes, you're correct for both! Thanks for pointing them out!