new lambda function
new switch option in lval_del for LVAL_FUN
modify LVAL_FUN case statement in lval_copy
rename function lval_expr_print to lval_print_expr
new lval_print_str function
modified LVAL_FUN case statment and added new LVAL_CASE statment in
lval_print
new lval_eq function
new LVAL_STR case in ltype_name
added e->par in lenv_new
new lval_copy
modified lenv_get
new lenv_def function
new builtin_lambda function