Added 'read_key' builtin that allows widget scripts to handle input

src/libsh/error.rs

@@ -87,6 +87,7 @@ pub trait ShResultExt {
   fn blame(self, span: Span) -> Self;
   fn try_blame(self, span: Span) -> Self;
 	fn promote_err(self, span: Span) -> Self;
+	fn is_flow_control(&self) -> bool;
 }
 
 impl<T> ShResultExt for Result<T, ShErr> {
@@ -101,6 +102,9 @@ impl<T> ShResultExt for Result<T, ShErr> {
 	fn promote_err(self, span: Span) -> Self {
 		self.map_err(|e| e.promote(span))
 	}
+	fn is_flow_control(&self) -> bool {
+		self.as_ref().is_err_and(|e| e.is_flow_control())
+	}
 }
 
 #[derive(Clone, Debug)]
@@ -179,6 +183,9 @@ impl ShErr {
 	pub fn simple(kind: ShErrKind, msg: impl Into<String>) -> Self {
 		Self { kind, src_span: None, labels: vec![], sources: vec![], notes: vec![msg.into()], io_guards: vec![] }
 	}
+	pub fn is_flow_control(&self) -> bool {
+		self.kind.is_flow_control()
+	}
 	pub fn promote(mut self, span: Span) -> Self {
 		if self.notes.is_empty() {
 			return self
@@ -356,6 +363,18 @@ pub enum ShErrKind {
   Null,
 }
 
+impl ShErrKind {
+	pub fn is_flow_control(&self) -> bool {
+		matches!(self,
+			Self::CleanExit(_) |
+			Self::FuncReturn(_) |
+			Self::LoopContinue(_) |
+			Self::LoopBreak(_) |
+			Self::ClearReadline
+		)
+	}
+}
+
 impl Display for ShErrKind {
   fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     let output = match self {