Recreated clean version of @leonerd:package-name-version

@leonerd and @rabbiveesh deleted this branch, but these changes are
really quite welcome (node tree was too flat with a package declaration
--i.e. namespace-- not wrapping the statements that follow)
so I've re-created just the relevant changes.

ganezdragon#12

Author: Leeft

grammar.js

@@ -219,7 +219,11 @@ module.exports = grammar({
     package_statement: $ => seq(
       'package',
       $.package_name,
-      $.semi_colon
+      optional(field('version', $.version)),
+      choice(
+        $.semi_colon,
+        field('body', $.block)
+      )
     ),
 
     ellipsis_statement: $ => seq(

test/corpus/package.txt

@@ -0,0 +1,55 @@
+=================================================
+Unit package statement
+=================================================
+
+package The::Package;
+
+---
+
+(source_file
+  (package_statement (package_name (identifier) (identifier)) (semi_colon))
+)
+
+=================================================
+Unit package statement with version
+=================================================
+
+package The::Package v1.23;
+
+---
+
+(source_file
+  (package_statement (package_name (identifier) (identifier)) (version) (semi_colon))
+)
+
+=================================================
+package block
+=================================================
+
+package The::Package {
+  ...
+}
+
+---
+
+(source_file
+  (package_statement (package_name (identifier) (identifier))
+    (block (ellipsis_statement))
+  )
+)
+
+=================================================
+package block with version
+=================================================
+
+package The::Package v4.56 {
+  ...
+}
+
+---
+
+(source_file
+  (package_statement (package_name (identifier) (identifier)) (version)
+    (block (ellipsis_statement))
+  )
+)