Screen keyboard API (iOS and Android change)

The iOS screen keyboard API was generalized by Philipp Wiesemann and
implemented on Android. I converted the existing iOS functions to the new
set:

SDL_bool SDL_HasScreenKeyboardSupport(SDL_Window * window)
– returns whether or not the onscreen keyboard is available for
the given window.
int SDL_ShowScreenKeyboard(SDL_Window * window)
– reveals the onscreen keyboard. Returns 0 on success and -1 on
error.
int SDL_HideScreenKeyboard(SDL_Window * window)
– hides the onscreen keyboard. Returns 0 on success and -1 on
error.
SDL_bool SDL_IsScreenKeyboardShown(SDL_Window * window)
– returns whether or not the onscreen keyboard is currently
visible.
int SDL_ToggleScreenKeyboard(SDL_Window * window)
– toggles the visibility of the onscreen keyboard. Returns 0 on
success and -1 on error.

Cheers!