feat!(argus-parser): complete parser

This changes the API for `ExprBuilder`, but that is OK.

argus-parser/examples/dump_expr.rs

@@ -0,0 +1,31 @@
+use std::env;
+
+use argus_parser::parse_str;
+use ariadne::{sources, Color, Label, Report, ReportKind};
+
+fn main() {
+    let src = env::args().nth(1).expect("Expected expression");
+
+    match parse_str(&src) {
+        Ok(expr) => println!("{:#?}", expr),
+        Err(errs) => {
+            errs.into_iter().for_each(|e| {
+                Report::build(ReportKind::Error, src.clone(), e.span().start)
+                    .with_message(e.to_string())
+                    .with_label(
+                        Label::new((src.clone(), e.span().into_range()))
+                            .with_message(e.reason().to_string())
+                            .with_color(Color::Red),
+                    )
+                    .with_labels(e.contexts().map(|(label, span)| {
+                        Label::new((src.clone(), span.into_range()))
+                            .with_message(format!("while parsing this {}", label))
+                            .with_color(Color::Yellow)
+                    }))
+                    .finish()
+                    .print(sources([(src.clone(), src.clone())]))
+                    .unwrap()
+            });
+        }
+    }
+}