Latex.ast_fun unexpected behaviour

[AbdallahS]

In the file src/lib/latex.ml, the function ast_fun behaves differently on x mod y than on x add y and other binary operators. This sounds strange to me and looks like a minor typo/bug.

I intend on updating the mod behaviour to match that of add and other arithmetic operators in my next patch (and then we can close this issue). If you'd rather not and tell me that the current behaviour is as intended, then I won't change it.

[AbdallahS]

Similarly, the function Latex.is_binary_op does not treat mod appropriately. Maybe mod was added later and the code wasn't updated. Unless told otherwise, I'll change this bit too.