split: Initial import

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>

----

Here is a split implementation.

I have a subsidiary project for testing (https://github.com/akiradeveloper/rust-split) where I compare my split with GNU split as a reference implementation in a way like QuickCheck.

Quick look at the performance says my split is twice slower than GNU one. Not desperate, and I will improve this later.
I think you should use ```stdin_raw()``` here instead of ```stdin()``` because ```stdin()``` already returns a ```BufferedReader```.