CoreIO and CoreConsole changes

[Steven Noonan]

I've split CoreIO into two classes: CoreIOReader and CoreIOWriter.

I did this so that classes which are write-only (TextWriter, for
example) don't have to privatize the buffer read functions. Classes
which need the old functionality (both CoreIOReader and CoreIOWriter at
once) can use multiple inheritance, or write a wrapper for using both
at once.

As a result of the aforementioned CoreIO changes, I've been able to
make CoreConsole better. It now can read from stdin and write to stdout
(previously, it was only able to read from stdout, since it inherited
CoreIO, a one-buffer class, and stdout is write-only).

I'm committing these changes in an hour or so. I just need to re-verify
the Doxygen documentation comments.

- Steven