The parser fails to parse strings with escaped quotation marks

Currently, escaped quotation marks within strings are interpreted as the end of a string.
For example, if show gave this:

    Foo "hello \" world!"

The parser would give back:

    > parseExprs "Foo \"hello \\\"world!\""
    ([Other "Foo ",StringLit "hello \\",Other "world!",StringLit ""],"")

instead of the expected

    ([Other "Foo ",StringLit "hello \\\" world!"],"")
