feat: add keyword of functions

add keyword "view" for functions, to record functions that don't change contract status after execution

input/JavaScriptLexer.g4

@@ -147,11 +147,15 @@ AtLeastOnce: 					'AT_LEAST_ONCE';
 AtMostOnce:                     'AT_MOST_ONCE';
 OnlyOnce:                       'ONLY_ONCE';
 
-// Event Global or Local
+/// Event Global or Local
 
 Global:                         'global';
 Local:                          'local';
 
+/// Function Type
+
+View:                           'view';
+
 /// Future Reserved Words
 
 Class:                          'class';

input/YJSParser.g4

@@ -63,11 +63,6 @@ clzOrFunctionDeclaration
 	|functionDeclaration
 	|eventDeclaration
 	;
-eventSemantics
-	:AtLeastOnce
-	|AtMostOnce
-	|OnlyOnce
-	;
 eventDeclaration
     :Event eventGlobalOrLocal? Identifier SemiColon
 	|Event eventGlobalOrLocal? Identifier '(' eventSemantics? ')' SemiColon
@@ -76,6 +71,11 @@ eventGlobalOrLocal
     :Global
     |Local
     ;
+eventSemantics
+	:AtLeastOnce
+	|AtMostOnce
+	|OnlyOnce
+	;
 sourceElement
     : statement
     ;
@@ -213,7 +213,7 @@ debuggerStatement
     ;
 
 functionDeclaration
-    : annotations? Export? Function Identifier '(' formalParameterList? ')' '{' functionBody '}'
+    : annotations? Export? Function Identifier '(' formalParameterList? ')' View '{' functionBody '}'
     ;
 
 classDeclaration