Move most of the root package into a subcrate. (#1445)

This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).

crates/nu-cli/src/commands/range.rs

@@ -0,0 +1,56 @@
+use crate::commands::WholeStreamCommand;
+use crate::context::CommandRegistry;
+use crate::deserializer::NumericRange;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{Signature, SyntaxShape};
+use nu_source::Tagged;
+
+#[derive(Deserialize)]
+struct RangeArgs {
+    area: Tagged<NumericRange>,
+}
+
+pub struct Range;
+
+impl WholeStreamCommand for Range {
+    fn name(&self) -> &str {
+        "range"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("range").required(
+            "rows ",
+            SyntaxShape::Range,
+            "range of rows to return: Eg) 4..7 (=> from 4 to 7)",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Return only the selected rows"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, range)?.run()
+    }
+}
+
+fn range(
+    RangeArgs { area }: RangeArgs,
+    RunnableContext { input, .. }: RunnableContext,
+) -> Result<OutputStream, ShellError> {
+    let range = area.item;
+    let (from, _) = range.from;
+    let (to, _) = range.to;
+
+    let from = *from as usize;
+    let to = *to as usize;
+
+    Ok(OutputStream::from_input(
+        input.values.skip(from).take(to - from + 1),
+    ))
+}