[Feature] Support double quotes in the expressions

[edwinyzh]

Not must-have, but nice to have, because it makes the code better to read when constructing the template scripts in Delphi code:

procedure TTestTemplateExpr.TestTernary;
begin
  Assert.AreEqual('a', Template.Eval('<% true?''a'':''b'' %>'));
  Assert.AreEqual('b', Template.Eval('<% false?''a'':''b'' %>'));

  // It'll be nice-to have if the above statements can be written as the following form:
  Assert.AreEqual('a', Template.Eval('<% true?"a":"b" %>'));
  Assert.AreEqual('b', Template.Eval('<% false?"a":"b" %>'));
end;

[edwinyzh]

Great! Thanks for the improvement!