peepmatic: Define fuzz targets for various parts of peepmatic

fuzz/fuzz_targets/peepmatic_parser.rs

@@ -0,0 +1,8 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use peepmatic_fuzzing::parser::parse;
+
+fuzz_target!(|data: &[u8]| {
+    parse(data);
+});