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/add-dist-funcs

Conflicts:
	src/stan/agrad/matrix.hpp
Merge branch 'develop' into feature/add-dist-funcs

Conflicts:
	src/stan/agrad/rev/matrix.hpp
	src/test/agrad/rev/matrix/squared_dist_test.cpp
	src/test/agrad/rev/matrix/squared_distance_test.cpp
	src/test/unit-agrad-rev/matrix/squared_dist_test.cpp
	src/test/unit/math/matrix/dist_test.cpp
	src/test/unit/math/matrix/squared_dist_test.cpp
adding tests; fixed bug in templated distance function
updating function signatures order
adding function signature test
adding function signature test
updating latex documentation for distance and squared_distance
Merge pull request #349 from stan-dev/feature/add-dist-funcs

Fixes #283.