adding more exeptions

[staxfur]

cpp-terminal is currently not checking that much for legal inputs on some functions. For example: Term::Window_24bit scr(0, 0, 10, 10); returns a segmentation fault, because the used vectors of the window class can't have negative places. we should simply throw a std::runtime_error here. That would include:

• Term::Window
• Term::Window_24bit
• (with some functions, like Term::Window::fill_bg)
• Term::color
• Term::color_24bit
  and probably all other functions without enforced types (like enums)