Provide support for accept_temporary_this modifier (#10)

* Allow accept_temporary_this modifier

Author: arturjpv

UnrealAngelscriptParser/Grammar/UnrealAngelscriptLexer.g4

@@ -82,6 +82,8 @@ Bool: 'bool';
 
 Auto: 'auto';
 
+AcceptTemporaryThis: 'accept_temporary_this';
+
 Access: 'access';
 
 Break: 'break';

UnrealAngelscriptParser/Grammar/UnrealAngelscriptParser.g4

@@ -429,7 +429,9 @@ declaratorDef:
 	declaratorid | declaratorDef (parametersAndQualifiers | LeftBracket constantExpression? RightBracket);
 
 parametersAndQualifiers:
-	LeftParen parameterDeclarationClause? RightParen Const? refqualifier?;
+	LeftParen parameterDeclarationClause? RightParen thisModifier? refqualifier?;
+
+thisModifier: Const | AcceptTemporaryThis;
 
 refqualifier: And | AndAnd;