Added new persistent sampler that does not change the chain state, useful for forward sampling using generated quanities only
Rename dist -> distance and squared_dist -> squared_distance, enable squared_distance in the modelling language and readd the reference documentation.
Missed %
Fixed header guard issue.
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
Merge branch 'develop' into feature/add-dist-funcs

Conflicts:
	src/stan/agrad/matrix.hpp
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 branch 'develop' of https://github.com/stan-dev/stan into develop
fixes issue #464
added diag_post_multiply to signatures and tested compilability
Merge branch 'develop' of https://github.com/stan-dev/stan into develop