enable list/dict access via square brackets in addtion to get/set() functions

[timobaumann]

DialogOS script is missing the feature mentioned in the title that is found in most languages. This is due to limitations of its lexer/parser which makes constructions like:

| exp:list LEPAREN number:accessor REPAREN
        {: RESULT = parser.createFunctionCall("get", createList(accessor).append(list); :}

hard to implement. It would, of course, be awesome if someone were to try this nonetheless.

See e.g. https://stackoverflow.com/questions/53679890/reduce-reduce-conflict-in-cup

[timobaumann]

note that structs can already be get/set using dot-notation: struct.field. However, it's not possible to add elements to the struct in this way.

[timobaumann]

the changes are now documented in the Wiki.