Revert "removed elt_divide and elt_multiply from function sig"
Revert "removed elt_divide and elt_multiply from function sig"

This reverts commit e4aba07dff6fff0e0260f1eee56f3690b9ccbab8.

stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math