add docs for fltk-sys
+/*!
+# fltk-sys
+
+Raw bindings for FLTK. These are generated using bindgen on the cfltk headers.
+
+## Usage
+```toml
+[dependencies]
+fltk-sys = "1.2"
+```
+
+Example code:
+```rust,no_run
+use fltk_sys::*;
+use std::os::raw::*;
+
+unsafe extern "C" fn cb(_wid: *mut button::Fl_Widget, data: *mut c_void) {
+ let frame = data as *mut frame::Fl_Box;
+ frame::Fl_Box_set_label(frame, "Hello World\0".as_ptr() as *const _);
+}
+
+fn main() {
+ unsafe {
+ fl::Fl_init_all();
+ image::Fl_register_images();
+ fl::Fl_lock();
+ let win = window::Fl_Window_new(100, 100, 400, 300, "Window\0".as_ptr() as *const _);
+ let frame = frame::Fl_Box_new(0, 0, 400, 200, std::ptr::null());
+ let but = button::Fl_Button_new(160, 220, 80, 40, "Click\0".as_ptr() as *const _);
+ window::Fl_Window_end(win);
+ window::Fl_Window_show(win);
+
+ button::Fl_Button_set_callback(but, Some(cb), frame as *mut _);
+
+ fl::Fl_run();
+ }
+}
+```
+
+## Dependencies
+CMake > 3.14, git and a C++11 compiler. The dev dependencies are basically the same as for [fltk-rs](https://github.com/fltk-rs/fltk-rs#dependencies).
+
+## Why you might want to use fltk-sys directly
+- If you need an abi stable cdylib that you can call into (as a plugin system for example).
+- To create your own wrapper around certain elements if you don't need the whole fltk crate.
+- fltk-sys, although memory and thread unsafe, is panic-safe.
+- You need a no-std gui library, in such case, you can replace the `std::` prefix with the `libc` via bindgen (requires adding libc as a dependency).
+- Wrapping a 3rd-party widget like in [fltk-flow](https://github.com/fltk-rs/fltk-flow).
+*/
#![allow(non_camel_case_types)]
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