New boolean setting `config.support_escapes` which defaults to false
(the historical behavior). When set to true, the following escapes are
handled:
* backslash doublequote -> doublequote
* backslash quote -> quote
* backslash n -> newline (ascii 10)
* backslash r -> carriage return (ascii 13)
* backslash backslash -> backslash
* backslash t -> tab (ascii 9)
This will solve #1645.