Allow double-quoted literals

When the allow double-quoted literals extension is enabled, Irie Pascal supports character and string literals enclosed with double quotation marks.

For example you could use

   "Hello world"

instead of

   'Hello world'

Double-quoted literals can be especially useful if you want to create literals that contain single quotes since you don't have to use two single quotes to represent one single quote.

For example you could create a string literal containing

   Don't go away

with the following:

   "Don't go away"

instead of

   'Don''t do away'