New scanner.c to better handle newlines

This imitates the Automatic Semicolon Insertions (ASI) done in
Javascript for Kotlin, to better deal with newlines that can cut
certain definitions and expressions in two.

This closes fwcd#32

test plan:
see new newlines.txt corpus test

Author: aryx

binding.gyp

@@ -8,6 +8,7 @@
       ],
       "sources": [
         "src/parser.c",
+        "src/scanner.c",
         "bindings/node/binding.cc"
       ],
       "cflags_c": [

grammar.js

@@ -103,6 +103,10 @@ module.exports = grammar({
     [$.user_type, $.function_type],
   ],
 
+  externals: $ => [
+    $._automatic_semicolon,
+  ],
+
   extras: $ => [
     $.comment,
     /\s+/ // Whitespace
@@ -135,7 +139,8 @@ module.exports = grammar({
       choice(
         seq("[", repeat1($._unescaped_annotation), "]"),
         $._unescaped_annotation
-      )
+      ),
+      $._semi
     ),
 
     package_header: $ => seq("package", $.identifier, $._semi),
@@ -542,9 +547,9 @@ module.exports = grammar({
 
     // See also https://github.com/tree-sitter/tree-sitter/issues/160
     // generic EOF/newline token
-    _semi: $ => /[\r\n]+/,
+    _semi: $ => choice($._automatic_semicolon, ';'),
 
-    _semis: $ => /[\r\n]+/,
+    _semis: $ => choice($._automatic_semicolon, ';'),
 
     assignment: $ => choice(
       prec.left(PREC.ASSIGNMENT, seq($.directly_assignable_expression, $._assignment_and_operator, $._expression)),