Add option to loremize arbitrary input from stdin

[jdpopkin]

I'd like it if I could pipe my own source texts into this program, since I have weird preferences for source texts. I'd be happy to try to make this change myself if anyone's interested.

The behavior would be something like
$ echo "This is a test!" | lorem --words 2 This is

[per9000]

Thanks for the feedback.

I had a look at your diff and it seemed OK -- but I was thinking that perhaps some sort of check on it would be nice. For example: there is nothing to read, there is too much to read, and so on. If you have time to improve it more that would be great.