added test case, update for src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java
added test case, update for #316
added test case, update for #316
"External Documentation Object" implemented (according to spec)

Depends on https://github.com/wordnik/swagger-core/pull/716
Make response headers available to the code generator (tryout)
MCA-specific extension

* template formatting methods
* remember last template execution context (to generate an output based on multiple specs)
* don't swallow exceptions
* write "x-mca" fields to Codegen classes