Fix compilation of fuzzer, make upgrade path for spans smoother, add CI

.github/workflows/fuzz.yml

@@ -10,10 +10,25 @@ on:
 jobs:
   check:
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./fuzz
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
-      - run: cd fuzz
-      - run: cargo check
+
+      - run: cargo fmt --all -- --check
+
+      - name: Check fuzz code compiles
+        run: cargo check
+
+      - name: Build AFL target
+        run: make setup-afl
+
+      - name: Build libfuzzer target
+        run: |
+          rustup toolchain install nightly
+          cargo install cargo-fuzz
+          cargo +nightly fuzz build main_libfuzzer

examples/tokenize_with_spans.rs

@@ -0,0 +1,12 @@
+//! Let's you easily try out the tokenizer with e.g.
+//! printf '<h1>Hello world!</h1>' | cargo run --example=tokenize_with_spans
+use html5gum::{DefaultEmitter, IoReader, Tokenizer};
+
+fn main() {
+    let emitter = DefaultEmitter::<usize>::new_with_span();
+    for token in
+        Tokenizer::new_with_emitter(IoReader::new(std::io::stdin().lock()), emitter).flatten()
+    {
+        println!("{:?}", token);
+    }
+}