moved tests for raise exception to no-main
test raise exception in model block
adding tests for model block behaviors
test that exception is thown in model block by calling that block (i.e. model's log_prob method) directly
test function that raises exception, called from model block
tests for called from transformed data block, all tests call model directly
tests for correct behaviour in all stan program blocks
fixed bug for raise_exception statement with multiple args
added code and tests to handle multiple args to raise_exception stmt
updated stan reference
cleanup
unit tests under test/unit/gm/raise_exception, models under test-models/no-main/gm/raise_exception
Merge branch 'develop' into feature/issue-748-stmt-raise-exception

Conflicts:
	doc/stan-reference-2.4.0.pdf
	make/tests
	src/stan/gm/generator.hpp
	src/test/test-models/no-main/gm/raise_ex_func_call_generated_quantities.stan
	src/test/test-models/no-main/gm/raise_ex_func_call_model.stan
	src/test/test-models/no-main/gm/raise_ex_func_call_transformed_data.stan
	src/test/test-models/no-main/gm/raise_ex_func_call_transformed_parameters.stan
	src/test/test-models/no-main/gm/raise_exception_generated_quantities.stan
	src/test/test-models/no-main/gm/raise_exception_transformed_data.stan
	src/test/test-models/no-main/gm/raise_exception_transformed_parameters.stan
Merge pull request #802 from stan-dev/feature/issue-748-stmt-raise-exception

Fixes #748. Feature/issue 748 stmt raise exception