Function imgui_sys::igImageButton

pub unsafe extern fn igImageButton(user_texture_id: ImTextureID,
                                   size: ImVec2,
                                   uv0: ImVec2,
                                   uv1: ImVec2,
                                   frame_padding: c_int,
                                   bg_col: ImVec4,
                                   tint_col: ImVec4)
                                   -> bool