Generalise Text::angle() logic

[wawuwo]

Hi!

I've rewritten Text::angle() to make it generic and able to handle any combination of mCos and mSin values. Before that Text::angle() could handle only three distinct cases and all other cases fell in "default", it was rather "stiff". I believe that is the reason why subcircuit symbol has text with wrong rotation angle.

It looks good now (at least on my machine):

May fix #765

[dsm]

Hi, why you don't use std::atan2 ?

It gives the exact angle and handle all quadrants.

[wawuwo]

@dsm thanks for the advice! I've rewritten it using the suggested function and the code looks much better and simpler now. The very existence of the tangent function had completely slipped out of my mind somehow and I chose that straightforward approach.

[ra3xdh]

Thanks for the fix! Merged.