Support for function Ctg is missing

[FoggyFinder]

It seems that support for function Ctg is missing. I think it makes sense to add it. I can do it, but I would like to know which option is better:

1. Replacing the function by tg when parsing (so, add ctg to the class Pseudo)
2. Implement full support

[cdrnet]

I don't think I've heard about ctg and tg functions. What are these about?

[FoggyFinder]

@cdrnet sorry, I meant
ctg - cotangents
tg - tangents

[cdrnet]

Ah, right. In Numerics we refer to them as tan and cot. Maybe there are different naming schemes?

Of course, I'm fine with adding them. If we add cot (or ctg), we may want to add sec and csc as well to get the full set (cot=1/tan, sec=1/cos, csc=1/sin).

[cdrnet]

So the remaining question is whether they shall be full expressions or just infix parsing magic. I'd vote to implement them fully and then maybe provide a routine later that simplifies all of them to sin and cos (on demand).

[FoggyFinder]

Next week, I'll think how can expand the module Trigonometric, so I will leave the issue open

[FoggyFinder]

#46