web scraping with css selectors (#2725)

* first step of making selector

* wip

* wip tests working

* probably good enough for a first pass

* oops, missed something.

* and something else...

* grrrr version errors

src/plugins/nu_plugin_extra_selector.rs

@@ -0,0 +1,6 @@
+use nu_plugin::serve_plugin;
+use nu_plugin_selector::Selector;
+
+fn main() {
+    serve_plugin(&mut Selector::new());
+}