Stream support (#812)

* Moves off of draining between filters. Instead, the sink will pull on the stream, and will drain element-wise. This moves the whole stream to being lazy.
* Adds ctrl-c support and connects it into some of the key points where we pull on the stream. If a ctrl-c is detect, we immediately halt pulling on the stream and return to the prompt.
* Moves away from having a SourceMap where anchor locations are stored. Now AnchorLocation is kept directly in the Tag.
* To make this possible, split tag and span. Span is largely used in the parser and is copyable. Tag is now no longer copyable.

src/commands/shells.rs

@@ -2,6 +2,7 @@ use crate::commands::WholeStreamCommand;
 use crate::data::TaggedDictBuilder;
 use crate::errors::ShellError;
 use crate::prelude::*;
+use std::sync::atomic::Ordering;
 
 pub struct Shells;
 
@@ -32,14 +33,14 @@ fn shells(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream
     let tag = args.call_info.name_tag;
 
     for (index, shell) in args.shell_manager.shells.lock().unwrap().iter().enumerate() {
-        let mut dict = TaggedDictBuilder::new(tag);
+        let mut dict = TaggedDictBuilder::new(&tag);
 
-        if index == args.shell_manager.current_shell {
+        if index == (*args.shell_manager.current_shell).load(Ordering::SeqCst) {
             dict.insert(" ", "X".to_string());
         } else {
             dict.insert(" ", " ".to_string());
         }
-        dict.insert("name", shell.name(&args.call_info.source_map));
+        dict.insert("name", shell.name());
         dict.insert("path", shell.path());
 
         shells_out.push_back(dict.into_tagged_value());