align readuntil and readline?

[JeffBezanson]

We changed readline to remove the trailing newline character by default, but readuntil still includes the delimiter. Arguably, they should behave the same.

readline also has a keyword argument chomp (defaulting to true) to control this. This is a slightly strange name, and is also very nearly a negative option (like saying "dont_include_delimiter=true"). This could be changed to keep, which would instead specify whether to keep the delimiter.