Extracting IO into its own file

in preparation for porting buffered io bits from pypy, mostly.  Also, it
took me awhile to find W_IOObject in the first place because I was
looking for a file with "io" in the name.
Merge pull request #484 from modcloth/mbh/extract-IO

Extracting IO into its own file
Merge branch 'master' of https://github.com/topazproject/topaz