Unified interface for autodiff'ing models
Fix model functional to work with higher-order autodiff by specifying template parameters; add test
Remove domain test for the moment
Use proper gradient template parameters
Merge branch 'develop' into feature/uniform_autodiff_pattern

Conflicts:
	.gitignore
	make/tests
	src/test/CmdStan/command_test.cpp
Merge pull request #459 from stan-dev/feature/uniform_autodiff_pattern

Feature/uniform autodiff pattern