better errors for keys without values

examples/tokens.rs

@@ -0,0 +1,16 @@
+use miette::{Context, IntoDiagnostic, Result};
+use std::env::args;
+use std::fs::read_to_string;
+use vdf_reader::Reader;
+
+fn main() -> Result<()> {
+    let path = args().nth(1).expect("no path provided");
+    let raw = read_to_string(path)
+        .into_diagnostic()
+        .wrap_err("failed to read input")?;
+    let reader = Reader::from(raw.as_str());
+    for event in reader {
+        println!("{:?}", event?);
+    }
+    Ok(())
+}