Allow C-style escapes in text input

[johnmyleswhite]

This closes #452 by making it possible to translate C-style escapes into their equivalents while reading in data from a DataFrame.

[simonster]

Obviously this doesn't handle all C-style escape sequences, but that seems fine, because I don't think anyone encodes their data as bell characters. But maybe this should also handle \\? Otherwise you run the risk of misinterpreting data with a correctly escaped backslash character in it.

[johnmyleswhite]

It seems reasonable to me to handle every single C-escape sequence. I just did enough to read in the file that was causing me trouble. Even the lowly bell character deserves some love.

[simonster]

Do we care about hex, octal, and Unicode escape sequences?

[johnmyleswhite]

Getting that right seemed non-trivial, which is why I bailed on it for the moment.

[johnmyleswhite]

Thanks for reviewing this, Simon!