Added modifyable output.

Still 9 lines, however you are able to change now what characters are printed out.
Just hand over two arguments:
`./life "\\" "."` for a backslash as "living cell" and a dot as dead cell.
If no arguments are given, the original version, with "X" and " ", is used.

Oh, and while adding this, I removed the compiler warnings. :)

Due to this, the weirdest combinations of characters is possible, and interesting patterns are created:

![bildschirmfoto 2013-12-01 um 12 19 04](https://f.cloud.github.com/assets/5861085/1650283/d7fb3a92-5a7a-11e3-9495-05fa8ba5f34a.png)
![bildschirmfoto 2013-12-01 um 12 21 33](https://f.cloud.github.com/assets/5861085/1650284/d7ff5190-5a7a-11e3-8638-7ab432eea9c1.png)
![bildschirmfoto 2013-12-01 um 12 22 00](https://f.cloud.github.com/assets/5861085/1650285/d8036ed8-5a7a-11e3-9f7e-3e1d17f99c97.png)


But nice work, no matter if you merge this or not :+1: