Support leptonica:1.83.0

I've had to disable doc tests because some of the syntax in the
autogenerated comments confuses it.

It looks like access to the PIX struct is now private, so we need to use
getters.

I started looking at this because of this issue in leptonica-plumbing
ccouzens/leptonica-plumbing#5

---

To test using my dev version of leptonica I need to use this command

```bash
LD_LIBRARY_PATH=../../DanBloomberg/leptonica/local/lib PKG_CONFIG_PATH=../../DanBloomberg/leptonica/local/lib/pkgconfig cargo test --lib
```

My checkout of leptonica was built with

```bash
sudo dnf builddep leptonica-devel
./autogen.sh
./configure --prefix
 /configure "--prefix=$(pwd)/local"
make
make install
```

.github/workflows/rust.yml

@@ -21,6 +21,6 @@ jobs:
     - name: Build
       run: cargo build --verbose
     - name: Run tests
-      run: cargo test --verbose
+      run: cargo test --verbose --lib
     - name: Check formatting
       run: cargo fmt -- --check

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "leptonica-sys"
-version = "0.4.2"
+version = "0.4.3"
 authors = ["Chris Couzens <[email protected]>"]
 edition = "2018"
 links = "lept"

src/lib.rs

@@ -6,16 +6,14 @@ include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
 
 #[cfg(test)]
 mod tests {
-    use super::{pixFreeData, pixRead};
-    use std::ffi::CStr;
+    use super::{pixFreeData, pixGetHeight, pixGetWidth, pixRead};
 
     #[test]
     fn image_size() {
         unsafe {
-            let image =
-                pixRead(CStr::from_bytes_with_nul_unchecked(b"../test image.png\0").as_ptr());
-            assert_eq!((*image).w, 1000);
-            assert_eq!((*image).h, 500);
+            let image = pixRead(b"../test image.png\0".as_ptr().cast());
+            assert_eq!(pixGetWidth(image), 1000);
+            assert_eq!(pixGetHeight(image), 500);
             pixFreeData(image);
         }
     }