[3.15] gh-157546: Add missing docstrings in curses (GH-157547)

[serhiy-storchaka]

The Python wrappers initscr() and start_color() now use the docstrings of the wrapped C functions. Also "WindowObject" in the initscr() docstring is replaced with "window object".

The newterm() wrapper and the screen type do not exist in this branch.
(cherry picked from commit b1e2766)

Co-authored-by: Serhiy Storchaka storchaka@gmail.com

• Issue: curses: initscr(), newterm(), start_color() and the screen type have no docstrings #157546

[serhiy-storchaka]

Only backported to 3.15: 3.13 and 3.14 lack several other docstrings (the window and panel types, the error exceptions), while the type docstrings were backported to the not yet released 3.15, so only these two functions are missing there.