Add parser README, some parser fixups

crates/nu-protocol/src/ty.rs

@@ -16,6 +16,7 @@ pub enum Type {
     Number,
     Nothing,
     Record(Vec<String>, Vec<Type>),
+    Table,
     ValueStream,
     Unknown,
     Error,
@@ -34,6 +35,7 @@ impl Display for Type {
             Type::Int => write!(f, "int"),
             Type::Range => write!(f, "range"),
             Type::Record(cols, vals) => write!(f, "record<{}, {:?}>", cols.join(", "), vals),
+            Type::Table => write!(f, "table"),
             Type::List(l) => write!(f, "list<{}>", l),
             Type::Nothing => write!(f, "nothing"),
             Type::Number => write!(f, "number"),