string content doesn't go through transformation. closes https://github.com/davidedc/livecodelab/issues/238

    # strings shouldn't undergo any transformation
    # so we use replace all the strings with
    # references to a table, which we'll replace back
    # later with the original strings.
    # This code is adapted from Processing.js
    # (ref: "codeWoStrings" and "injectStrings")