Support :!~ symbols, add symbol test cases (#153)

* Support :!~ symbols, add symbol test cases

This commit updates the lexer to specifically match the symbol :!~.

I also add test cases from
https://github.com/ruby/spec/blob/master/language/symbol_spec.rb:

- :_
- :!~
- :''

Fixes #143.

* fixup! Support :!~ symbols, add symbol test cases

src/scanner.cc

@@ -280,18 +280,23 @@ struct Scanner {
         }
         return false;
 
-      // &, ^, |, ~, /, %, !,`
+      // &, ^, |, ~, /, %`
       case '&':
       case '^':
       case '|':
       case '~':
       case '/':
       case '%':
-      case '!':
       case '`':
         advance(lexer);
         return true;
 
+      // !, !=, !~
+      case '!':
+        advance(lexer);
+        if (lexer->lookahead == '=' || lexer->lookahead == '~') advance(lexer);
+        return true;
+
       // *, **
       case '*':
         advance(lexer);
@@ -316,6 +321,7 @@ struct Scanner {
   }
 
   bool scan_symbol_identifier(TSLexer *lexer) {
+
     if (lexer->lookahead == '@') {
       advance(lexer);
       if (lexer->lookahead == '@') {

test/corpus/literals.txt

@@ -13,6 +13,7 @@ symbol
 :$0
 :_bar
 :åäö
+:_
 
 ---
 
@@ -27,6 +28,7 @@ symbol
   (simple_symbol)
   (simple_symbol)
   (simple_symbol)
+  (simple_symbol)
   (simple_symbol))
 
 ======
@@ -59,6 +61,8 @@ symbol operators
 :<=
 :<<
 :<=>
+:!=
+:!~
 
 ---
 
@@ -88,18 +92,22 @@ symbol operators
   (simple_symbol)
   (simple_symbol)
   (simple_symbol)
+  (simple_symbol)
+  (simple_symbol)
   (simple_symbol))
 
 ====================
 single quoted symbol
 ====================
 
+:''
 :'foo bar'
 :'#{'
 
 ---
 
 (program
+  (delimited_symbol)
   (delimited_symbol (string_content))
   (delimited_symbol (string_content)))