Add material about the "r" and "u" prefixes for string literals; should be reviewed for clarity.
Add material about the "r" and "u" prefixes for string literals; should
be reviewed for clarity.

Work around a bogosity in the HTML version of the escape sequences table
conversion.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator