added operator/ to doc
added columns and rows dot product
added rows and columns dot self to doc
added columns/rows dot_produt and dot_self
removed elt_divide and elt_multiply from function sig
added rows_dot_self to math/matrix.hpp
added more tests to fvar_matrix_test
added compiled models test for columns/rows dot_product and dot_self
added mdivide_left_tri_low with tests to fvar/matrix
added mdivide_right_tri_low with tests to fvar/matrix
added rows_dot_self to matrix with test
added compile test for rows_dot_product
Revert "removed elt_divide and elt_multiply from function sig"

This reverts commit e4aba07dff6fff0e0260f1eee56f3690b9ccbab8.
Revert "Revert "removed elt_divide and elt_multiply from function sig""

This reverts commit ce64bbc833fdb81d33efb9f8f9d316c21459654a.
Revert "Revert "Revert "removed elt_divide and elt_multiply from function sig"""

This reverts commit a153d7ed29306f10fe81fed56989e19fef66ef14.
added rows dot product and self to model_header
fixed columns and rows dot prod and dot self in function sig
removed compiled models test for columns and rows dot_product and dot_self

causes unit-test fail...