Fix issue where certain files would cause Errno::EPIPE exception to be raised

[abrom]

Fixes #7

Use Open3 instead of IO library for calling to Tika.

[abrom]

FYI @rywall. Keeps the default still using the IO pipe method, but allows you to use the Ruby Shell alternative with an initialiser param (or via the class .read method).

[rywall]

@abrom perfect, thanks!

[abrom]

@rywall I was having some major flake issues with the solution I'd originally come up with. So I've gone back to the drawing board and come up with another solution that appears to be able to read your problem file without any errors.

I've tested it on a bunch of my files as far as I can tell it's all looking good..

However I'd really like to get your input on whether this works for you on a larger set of data before merging. Can you please check this branch out and try it on some of the other files you've previously had problems with (and of course check that there aren't any regressions).