add optional sigil % to start of commands (#248)

Author: Tyarel8

grammar.js

@@ -1569,7 +1569,7 @@ function _command_rule(parenthesized) {
     return prec.right(
       seq(
         choice(
-          field('head', seq(optional('^'), $.cmd_identifier)),
+          field('head', seq(optional(choice('^', '%')), $.cmd_identifier)),
           field('head', seq('^', $._stringish)),
         ),
         repeat(seq(sep, optional($._cmd_arg))),

queries/nu/highlights.scm

@@ -305,7 +305,10 @@ key: (identifier) @property
   (#eq? @keyword "as"))
 
 (command
-  "^" @punctuation.delimiter
+  [
+  "^"
+  "%"
+  ] @punctuation.delimiter
   head: (_) @function)
 
 "where" @function.builtin