Backslash escaping

This is a fix to a bug in zvm that causes any backslashes in the story output to be considered as escape characters. `\n` produces a newline, `\\` shows only one backslash etc. `\'` crashes Parchment completely. See http://iplayif.com/?story=https://dl.dropbox.com/u/27567916/test.z8 for a test case.