Added new persistent sampler that does not change the chain state, useful for forward sampling using generated quanities only
Merge pull request #324 from stan-dev/hotfix/v2.0.1

Hotfix/v2.0.1
Merge branch 'develop' into feature/persistent_sampler

Conflicts:
	make/tests
Fix broken test, update doc
making test clearer
Changed name from persistent sampler to fixed parameter sampler
Merge branch 'develop' into feature/persistent_sampler
Updated tests
Merge branch 'feature/persistent_sampler' of github.com:stan-dev/stan into feature/persistent_sampler

Conflicts:
	src/test/mcmc/fixed_param_sampler_test.cpp
Working empty sampler test
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
Merge pull request #461 from stan-dev/release/v2.1.0

Release/v2.1.0
switched to arena malloc to fix #472
added stack_alloc::bytes_allocated and test
added bytes allocated test to softmax test
getting stack_alloc to work under Windows
Merge branch 'master' of https://github.com/stan-dev/stan into hotfix/v2.1.1
Added method to inspect the size of the stack. Added test for softmax checking that all elements were allocated to the correct stack.